updater/install.c

/*
 * Copyright (C) 2009 The Android Open Source Project
 * Copyright (c) 2010, Code Aurora Forum. All rights reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include <ctype.h>
#include <errno.h>
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mount.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>

#include "cutils/misc.h"
#include "cutils/properties.h"
#include "edify/expr.h"
#include "mincrypt/sha.h"
#include "minzip/DirUtil.h"
#include "mounts.h"
#include "flashutils/flashutils.h"
#include "mtdutils/mtdutils.h"
#include "mmcutils/mmcutils.h"
#include "updater.h"
#include "applypatch/applypatch.h"

// mount(type, location, mount_point)
//
//   what:  type="MTD"   location="<partition>"            to mount a yaffs2 filesystem
//          type="vfat"  location="/dev/block/<whatever>"  to mount a device
Value* MountFn(const char* name, State* state, int argc, Expr* argv[]) {
    char* result = NULL;
    if (argc != 3) {
        return ErrorAbort(state, "%s() expects 3 args, got %d", name, argc);
    }
    char* type;
    char* location;
    char* mount_point;
    if (ReadArgs(state, argv, 3, &type, &location, &mount_point) < 0) {
        return NULL;
    }

    if (strlen(type) == 0) {
        ErrorAbort(state, "type argument to %s() can't be empty", name);
        goto done;
    }
    if (strlen(location) == 0) {
        ErrorAbort(state, "location argument to %s() can't be empty", name);
        goto done;
    }
    if (strlen(mount_point) == 0) {
        ErrorAbort(state, "mount_point argument to %s() can't be empty", name);
        goto done;
    }

    mkdir(mount_point, 0755);

    if (strcmp(type, "MTD") == 0 || strcmp(type, "MMC") == 0) {
        if (0 == mount_partition(location, mount_point, get_default_filesystem(), 0))
            result = mount_point;
        else
            result = strdup("");
    } else {
        if (mount(location, mount_point, type,
                  MS_NOATIME | MS_NODEV | MS_NODIRATIME, "") < 0) {
            fprintf(stderr, "%s: failed to mount %s at %s: %s\n",
                    name, location, mount_point, strerror(errno));
            result = strdup("");
        } else {
            result = mount_point;
        }
    }

done:
    free(type);
    free(location);
    if (result != mount_point) free(mount_point);
    return StringValue(result);
}


// is_mounted(mount_point)
Value* IsMountedFn(const char* name, State* state, int argc, Expr* argv[]) {
    char* result = NULL;
    if (argc != 1) {
        return ErrorAbort(state, "%s() expects 1 arg, got %d", name, argc);
    }
    char* mount_point;
    if (ReadArgs(state, argv, 1, &mount_point) < 0) {
        return NULL;
    }
    if (strlen(mount_point) == 0) {
        ErrorAbort(state, "mount_point argument to unmount() can't be empty");
        goto done;
    }

    scan_mounted_volumes();
    const MountedVolume* vol = find_mounted_volume_by_mount_point(mount_point);
    if (vol == NULL) {
        result = strdup("");
    } else {
        result = mount_point;
    }

done:
    if (result != mount_point) free(mount_point);
    return StringValue(result);
}


Value* UnmountFn(const char* name, State* state, int argc, Expr* argv[]) {
    char* result = NULL;
    if (argc != 1) {
        return ErrorAbort(state, "%s() expects 1 arg, got %d", name, argc);
    }
    char* mount_point;
    if (ReadArgs(state, argv, 1, &mount_point) < 0) {
        return NULL;
    }
    if (strlen(mount_point) == 0) {
        ErrorAbort(state, "mount_point argument to unmount() can't be empty");
        goto done;
    }

    scan_mounted_volumes();
    const MountedVolume* vol = find_mounted_volume_by_mount_point(mount_point);
    if (vol == NULL) {
        fprintf(stderr, "unmount of %s failed; no such volume\n", mount_point);
        result = strdup("");
    } else {
        unmount_mounted_volume(vol);
        result = mount_point;
    }

done:
    if (result != mount_point) free(mount_point);
    return StringValue(result);
}


// format(type, location)
//
//    type="MTD"  location=partition
Value* FormatFn(const char* name, State* state, int argc, Expr* argv[]) {
    char* result = NULL;
    if (argc != 2) {
        return ErrorAbort(state, "%s() expects 2 args, got %d", name, argc);
    }
    char* type;
    char* location;
    if (ReadArgs(state, argv, 2, &type, &location) < 0) {
        return NULL;
    }

    if (strlen(type) == 0) {
        ErrorAbort(state, "type argument to %s() can't be empty", name);
        goto done;
    }
    if (strlen(location) == 0) {
        ErrorAbort(state, "location argument to %s() can't be empty", name);
        goto done;
    }

    if (strcmp(type, "MTD") == 0 || strcmp(type, "MMC") == 0) {
        if (0 != erase_partition(location, NULL)) {
            result = strdup("");
            goto done;
        }
    } else {
        fprintf(stderr, "%s: unsupported type \"%s\"", name, type);
    }
    result = location;
done:
    free(type);
    if (result != location) free(location);
    return StringValue(result);
}


Value* DeleteFn(const char* name, State* state, int argc, Expr* argv[]) {
    char** paths = malloc(argc * sizeof(char*));
    int i;
    for (i = 0; i < argc; ++i) {
        paths[i] = Evaluate(state, argv[i]);
        if (paths[i] == NULL) {
            int j;
            for (j = 0; j < i; ++i) {
                free(paths[j]);
            }
            free(paths);
            return NULL;
        }
    }

    bool recursive = (strcmp(name, "delete_recursive") == 0);

    int success = 0;
    for (i = 0; i < argc; ++i) {
        if ((recursive ? dirUnlinkHierarchy(paths[i]) : unlink(paths[i])) == 0)
            ++success;
        free(paths[i]);
    }
    free(paths);

    char buffer[10];
    sprintf(buffer, "%d", success);
    return StringValue(strdup(buffer));
}


Value* ShowProgressFn(const char* name, State* state, int argc, Expr* argv[]) {
    if (argc != 2) {
        return ErrorAbort(state, "%s() expects 2 args, got %d", name, argc);
    }
    char* frac_str;
    char* sec_str;
    if (ReadArgs(state, argv, 2, &frac_str, &sec_str) < 0) {
        return NULL;
    }

    double frac = strtod(frac_str, NULL);
    int sec = strtol(sec_str, NULL, 10);

    UpdaterInfo* ui = (UpdaterInfo*)(state->cookie);
    fprintf(ui->cmd_pipe, "progress %f %d\n", frac, sec);

    free(sec_str);
    return StringValue(frac_str);
}

Value* SetProgressFn(const char* name, State* state, int argc, Expr* argv[]) {
    if (argc != 1) {
        return ErrorAbort(state, "%s() expects 1 arg, got %d", name, argc);
    }
    char* frac_str;
    if (ReadArgs(state, argv, 1, &frac_str) < 0) {
        return NULL;
    }

    double frac = strtod(frac_str, NULL);

    UpdaterInfo* ui = (UpdaterInfo*)(state->cookie);
    fprintf(ui->cmd_pipe, "set_progress %f\n", frac);

    return StringValue(frac_str);
}

// package_extract_dir(package_path, destination_path)
Value* PackageExtractDirFn(const char* name, State* state,
                          int argc, Expr* argv[]) {
    if (argc != 2) {
        return ErrorAbort(state, "%s() expects 2 args, got %d", name, argc);
    }
    char* zip_path;
    char* dest_path;
    if (ReadArgs(state, argv, 2, &zip_path, &dest_path) < 0) return NULL;

    ZipArchive* za = ((UpdaterInfo*)(state->cookie))->package_zip;

    // To create a consistent system image, never use the clock for timestamps.
    struct utimbuf timestamp = { 1217592000, 1217592000 };  // 8/1/2008 default

    bool success = mzExtractRecursive(za, zip_path, dest_path,
                                      MZ_EXTRACT_FILES_ONLY, &timestamp,
                                      NULL, NULL);
    free(zip_path);
    free(dest_path);
    return StringValue(strdup(success ? "t" : ""));
}


// package_extract_file(package_path, destination_path)
//   or
// package_extract_file(package_path)
//   to return the entire contents of the file as the result of this
//   function (the char* returned is actually a FileContents*).
Value* PackageExtractFileFn(const char* name, State* state,
                           int argc, Expr* argv[]) {
    if (argc != 1 && argc != 2) {
        return ErrorAbort(state, "%s() expects 1 or 2 args, got %d",
                          name, argc);
    }
    bool success = false;
    if (argc == 2) {
        // The two-argument version extracts to a file.

        char* zip_path;
        char* dest_path;
        if (ReadArgs(state, argv, 2, &zip_path, &dest_path) < 0) return NULL;

        ZipArchive* za = ((UpdaterInfo*)(state->cookie))->package_zip;
        const ZipEntry* entry = mzFindZipEntry(za, zip_path);
        if (entry == NULL) {
            fprintf(stderr, "%s: no %s in package\n", name, zip_path);
            goto done2;
        }

        FILE* f = fopen(dest_path, "wb");
        if (f == NULL) {
            fprintf(stderr, "%s: can't open %s for write: %s\n",
                    name, dest_path, strerror(errno));
            goto done2;
        }
        success = mzExtractZipEntryToFile(za, entry, fileno(f));
        fclose(f);

      done2:
        free(zip_path);
        free(dest_path);
        return StringValue(strdup(success ? "t" : ""));
    } else {
        // The one-argument version returns the contents of the file
        // as the result.

        char* zip_path;
        Value* v = malloc(sizeof(Value));
        v->type = VAL_BLOB;
        v->size = -1;
        v->data = NULL;

        if (ReadArgs(state, argv, 1, &zip_path) < 0) return NULL;

        ZipArchive* za = ((UpdaterInfo*)(state->cookie))->package_zip;
        const ZipEntry* entry = mzFindZipEntry(za, zip_path);
        if (entry == NULL) {
            fprintf(stderr, "%s: no %s in package\n", name, zip_path);
            goto done1;
        }

        v->size = mzGetZipEntryUncompLen(entry);
        v->data = malloc(v->size);
        if (v->data == NULL) {
            fprintf(stderr, "%s: failed to allocate %ld bytes for %s\n",
                    name, (long)v->size, zip_path);
            goto done1;
        }

        success = mzExtractZipEntryToBuffer(za, entry,
                                            (unsigned char *)v->data);

      done1:
        free(zip_path);
        if (!success) {
            free(v->data);
            v->data = NULL;
            v->size = -1;
        }
        return v;
    }
}


// symlink target src1 src2 ...
//    unlinks any previously existing src1, src2, etc before creating symlinks.
Value* SymlinkFn(const char* name, State* state, int argc, Expr* argv[]) {
    if (argc == 0) {
        return ErrorAbort(state, "%s() expects 1+ args, got %d", name, argc);
    }
    char* target;
    target = Evaluate(state, argv[0]);
    if (target == NULL) return NULL;

    char** srcs = ReadVarArgs(state, argc-1, argv+1);
    if (srcs == NULL) {
        free(target);
        return NULL;
    }

    int i;
    for (i = 0; i < argc-1; ++i) {
        if (unlink(srcs[i]) < 0) {
            if (errno != ENOENT) {
                fprintf(stderr, "%s: failed to remove %s: %s\n",
                        name, srcs[i], strerror(errno));
            }
        }
        if (symlink(target, srcs[i]) < 0) {
            fprintf(stderr, "%s: failed to symlink %s to %s: %s\n",
                    name, srcs[i], target, strerror(errno));
        }
        free(srcs[i]);
    }
    free(srcs);
    return StringValue(strdup(""));
}


Value* SetPermFn(const char* name, State* state, int argc, Expr* argv[]) {
    char* result = NULL;
    bool recursive = (strcmp(name, "set_perm_recursive") == 0);

    int min_args = 4 + (recursive ? 1 : 0);
    if (argc < min_args) {
        return ErrorAbort(state, "%s() expects %d+ args, got %d", name, argc);
    }

    char** args = ReadVarArgs(state, argc, argv);
    if (args == NULL) return NULL;

    char* end;
    int i;

    int uid = strtoul(args[0], &end, 0);
    if (*end != '\0' || args[0][0] == 0) {
        ErrorAbort(state, "%s: \"%s\" not a valid uid", name, args[0]);
        goto done;
    }

    int gid = strtoul(args[1], &end, 0);
    if (*end != '\0' || args[1][0] == 0) {
        ErrorAbort(state, "%s: \"%s\" not a valid gid", name, args[1]);
        goto done;
    }

    if (recursive) {
        int dir_mode = strtoul(args[2], &end, 0);
        if (*end != '\0' || args[2][0] == 0) {
            ErrorAbort(state, "%s: \"%s\" not a valid dirmode", name, args[2]);
            goto done;
        }

        int file_mode = strtoul(args[3], &end, 0);
        if (*end != '\0' || args[3][0] == 0) {
            ErrorAbort(state, "%s: \"%s\" not a valid filemode",
                       name, args[3]);
            goto done;
        }

        for (i = 4; i < argc; ++i) {
            dirSetHierarchyPermissions(args[i], uid, gid, dir_mode, file_mode);
        }
    } else {
        int mode = strtoul(args[2], &end, 0);
        if (*end != '\0' || args[2][0] == 0) {
            ErrorAbort(state, "%s: \"%s\" not a valid mode", name, args[2]);
            goto done;
        }

        for (i = 3; i < argc; ++i) {
            if (chown(args[i], uid, gid) < 0) {
                fprintf(stderr, "%s: chown of %s to %d %d failed: %s\n",
                        name, args[i], uid, gid, strerror(errno));
            }
            if (chmod(args[i], mode) < 0) {
                fprintf(stderr, "%s: chmod of %s to %o failed: %s\n",
                        name, args[i], mode, strerror(errno));
            }
        }
    }
    result = strdup("");

done:
    for (i = 0; i < argc; ++i) {
        free(args[i]);
    }
    free(args);

    return StringValue(result);
}


Value* GetPropFn(const char* name, State* state, int argc, Expr* argv[]) {
    if (argc != 1) {
        return ErrorAbort(state, "%s() expects 1 arg, got %d", name, argc);
    }
    char* key;
    key = Evaluate(state, argv[0]);
    if (key == NULL) return NULL;

    char value[PROPERTY_VALUE_MAX];
    property_get(key, value, "");
    free(key);

    return StringValue(strdup(value));
}


// file_getprop(file, key)
//
//   interprets 'file' as a getprop-style file (key=value pairs, one
//   per line, # comment lines and blank lines okay), and returns the value
//   for 'key' (or "" if it isn't defined).
Value* FileGetPropFn(const char* name, State* state, int argc, Expr* argv[]) {
    char* result = NULL;
    char* buffer = NULL;
    char* filename;
    char* key;
    if (ReadArgs(state, argv, 2, &filename, &key) < 0) {
        return NULL;
    }

    struct stat st;
    if (stat(filename, &st) < 0) {
        ErrorAbort(state, "%s: failed to stat \"%s\": %s",
                   name, filename, strerror(errno));
        goto done;
    }

#define MAX_FILE_GETPROP_SIZE    65536

    if (st.st_size > MAX_FILE_GETPROP_SIZE) {
        ErrorAbort(state, "%s too large for %s (max %d)",
                   filename, name, MAX_FILE_GETPROP_SIZE);
        goto done;
    }

    buffer = malloc(st.st_size+1);
    if (buffer == NULL) {
        ErrorAbort(state, "%s: failed to alloc %d bytes", name, st.st_size+1);
        goto done;
    }

    FILE* f = fopen(filename, "rb");
    if (f == NULL) {
        ErrorAbort(state, "%s: failed to open %s: %s",
                   name, filename, strerror(errno));
        goto done;
    }

    if (fread(buffer, 1, st.st_size, f) != st.st_size) {
        ErrorAbort(state, "%s: failed to read %d bytes from %s",
                   name, st.st_size+1, filename);
        fclose(f);
        goto done;
    }
    buffer[st.st_size] = '\0';

    fclose(f);

    char* line = strtok(buffer, "\n");
    do {
        // skip whitespace at start of line
        while (*line && isspace(*line)) ++line;

        // comment or blank line: skip to next line
        if (*line == '\0' || *line == '#') continue;

        char* equal = strchr(line, '=');
        if (equal == NULL) {
            ErrorAbort(state, "%s: malformed line \"%s\": %s not a prop file?",
                       name, line, filename);
            goto done;
        }

        // trim whitespace between key and '='
        char* key_end = equal-1;
        while (key_end > line && isspace(*key_end)) --key_end;
        key_end[1] = '\0';

        // not the key we're looking for
        if (strcmp(key, line) != 0) continue;

        // skip whitespace after the '=' to the start of the value
        char* val_start = equal+1;
        while(*val_start && isspace(*val_start)) ++val_start;

        // trim trailing whitespace
        char* val_end = val_start + strlen(val_start)-1;
        while (val_end > val_start && isspace(*val_end)) --val_end;
        val_end[1] = '\0';

        result = strdup(val_start);
        break;

    } while ((line = strtok(NULL, "\n")));

    if (result == NULL) result = strdup("");

  done:
    free(filename);
    free(key);
    free(buffer);
    return StringValue(result);
}


static bool write_raw_image_cb(const unsigned char* data,
                               int data_len, void* ctx) {
    int r = mtd_write_data((MtdWriteContext*)ctx, (const char *)data, data_len);
    if (r == data_len) return true;
    fprintf(stderr, "%s\n", strerror(errno));
    return false;
}

// write_raw_image(file, partition)
Value* WriteRawImageFn(const char* name, State* state, int argc, Expr* argv[]) {
    char* result = NULL;

    char* partition;
    char* filename;
    if (ReadArgs(state, argv, 2, &filename, &partition) < 0) {
        return NULL;
    }

    if (strlen(partition) == 0) {
        ErrorAbort(state, "partition argument to %s can't be empty", name);
        goto done;
    }
    if (strlen(filename) == 0) {
        ErrorAbort(state, "file argument to %s can't be empty", name);
        goto done;
    }

    if (0 == restore_raw_partition(partition, filename))
        result = strdup(partition);
    else
        result = strdup("");

done:
    if (result != partition) free(partition);
    free(filename);
    return StringValue(result);
}

// apply_patch_space(bytes)
Value* ApplyPatchSpaceFn(const char* name, State* state,
                         int argc, Expr* argv[]) {
    char* bytes_str;
    if (ReadArgs(state, argv, 1, &bytes_str) < 0) {
        return NULL;
    }

    char* endptr;
    size_t bytes = strtol(bytes_str, &endptr, 10);
    if (bytes == 0 && endptr == bytes_str) {
        ErrorAbort(state, "%s(): can't parse \"%s\" as byte count\n\n",
                   name, bytes_str);
        free(bytes_str);
        return NULL;
    }

    return StringValue(strdup(CacheSizeCheck(bytes) ? "" : "t"));
}


// apply_patch(srcfile, tgtfile, tgtsha1, tgtsize, sha1_1, patch_1, ...)
Value* ApplyPatchFn(const char* name, State* state, int argc, Expr* argv[]) {
    if (argc < 6 || (argc % 2) == 1) {
        return ErrorAbort(state, "%s(): expected at least 6 args and an "
                                 "even number, got %d",
                          name, argc);
    }

    char* source_filename;
    char* target_filename;
    char* target_sha1;
    char* target_size_str;
    if (ReadArgs(state, argv, 4, &source_filename, &target_filename,
                 &target_sha1, &target_size_str) < 0) {
        return NULL;
    }

    char* endptr;
    size_t target_size = strtol(target_size_str, &endptr, 10);
    if (target_size == 0 && endptr == target_size_str) {
        ErrorAbort(state, "%s(): can't parse \"%s\" as byte count",
                   name, target_size_str);
        free(source_filename);
        free(target_filename);
        free(target_sha1);
        free(target_size_str);
        return NULL;
    }

    int patchcount = (argc-4) / 2;
    Value** patches = ReadValueVarArgs(state, argc-4, argv+4);

    int i;
    for (i = 0; i < patchcount; ++i) {
        if (patches[i*2]->type != VAL_STRING) {
            ErrorAbort(state, "%s(): sha-1 #%d is not string", name, i);
            break;
        }
        if (patches[i*2+1]->type != VAL_BLOB) {
            ErrorAbort(state, "%s(): patch #%d is not blob", name, i);
            break;
        }
    }
    if (i != patchcount) {
        for (i = 0; i < patchcount*2; ++i) {
            FreeValue(patches[i]);
        }
        free(patches);
        return NULL;
    }

    char** patch_sha_str = malloc(patchcount * sizeof(char*));
    for (i = 0; i < patchcount; ++i) {
        patch_sha_str[i] = patches[i*2]->data;
        patches[i*2]->data = NULL;
        FreeValue(patches[i*2]);
        patches[i] = patches[i*2+1];
    }

    int result = applypatch(source_filename, target_filename,
                            target_sha1, target_size,
                            patchcount, patch_sha_str, patches);

    for (i = 0; i < patchcount; ++i) {
        FreeValue(patches[i]);
    }
    free(patch_sha_str);
    free(patches);

    return StringValue(strdup(result == 0 ? "t" : ""));
}

// apply_patch_check(file, [sha1_1, ...])
Value* ApplyPatchCheckFn(const char* name, State* state,
                         int argc, Expr* argv[]) {
    if (argc < 1) {
        return ErrorAbort(state, "%s(): expected at least 1 arg, got %d",
                          name, argc);
    }

    char* filename;
    if (ReadArgs(state, argv, 1, &filename) < 0) {
        return NULL;
    }

    int patchcount = argc-1;
    char** sha1s = ReadVarArgs(state, argc-1, argv+1);

    int result = applypatch_check(filename, patchcount, sha1s);

    int i;
    for (i = 0; i < patchcount; ++i) {
        free(sha1s[i]);
    }
    free(sha1s);

    return StringValue(strdup(result == 0 ? "t" : ""));
}

Value* UIPrintFn(const char* name, State* state, int argc, Expr* argv[]) {
    char** args = ReadVarArgs(state, argc, argv);
    if (args == NULL) {
        return NULL;
    }

    int size = 0;
    int i;
    for (i = 0; i < argc; ++i) {
        size += strlen(args[i]);
    }
    char* buffer = malloc(size+1);
    size = 0;
    for (i = 0; i < argc; ++i) {
        strcpy(buffer+size, args[i]);
        size += strlen(args[i]);
        free(args[i]);
    }
    free(args);
    buffer[size] = '\0';

    char* line = strtok(buffer, "\n");
    while (line) {
        fprintf(((UpdaterInfo*)(state->cookie))->cmd_pipe,
                "ui_print %s\n", line);
        line = strtok(NULL, "\n");
    }
    fprintf(((UpdaterInfo*)(state->cookie))->cmd_pipe, "ui_print\n");

    return StringValue(buffer);
}

Value* RunProgramFn(const char* name, State* state, int argc, Expr* argv[]) {
    if (argc < 1) {
        return ErrorAbort(state, "%s() expects at least 1 arg", name);
    }
    char** args = ReadVarArgs(state, argc, argv);
    if (args == NULL) {
        return NULL;
    }

    char** args2 = malloc(sizeof(char*) * (argc+1));
    memcpy(args2, args, sizeof(char*) * argc);
    args2[argc] = NULL;

    fprintf(stderr, "about to run program [%s] with %d args\n", args2[0], argc);

    pid_t child = fork();
    if (child == 0) {
        execv(args2[0], args2);
        fprintf(stderr, "run_program: execv failed: %s\n", strerror(errno));
        _exit(1);
    }
    int status;
    waitpid(child, &status, 0);
    if (WIFEXITED(status)) {
        if (WEXITSTATUS(status) != 0) {
            fprintf(stderr, "run_program: child exited with status %d\n",
                    WEXITSTATUS(status));
        }
    } else if (WIFSIGNALED(status)) {
        fprintf(stderr, "run_program: child terminated by signal %d\n",
                WTERMSIG(status));
    }

    int i;
    for (i = 0; i < argc; ++i) {
        free(args[i]);
    }
    free(args);
    free(args2);

    char buffer[20];
    sprintf(buffer, "%d", status);

    return StringValue(strdup(buffer));
}

// Take a sha-1 digest and return it as a newly-allocated hex string.
static char* PrintSha1(uint8_t* digest) {
    char* buffer = malloc(SHA_DIGEST_SIZE*2 + 1);
    int i;
    const char* alphabet = "0123456789abcdef";
    for (i = 0; i < SHA_DIGEST_SIZE; ++i) {
        buffer[i*2] = alphabet[(digest[i] >> 4) & 0xf];
        buffer[i*2+1] = alphabet[digest[i] & 0xf];
    }
    buffer[i*2] = '\0';
    return buffer;
}

// sha1_check(data)
//    to return the sha1 of the data (given in the format returned by
//    read_file).
//
// sha1_check(data, sha1_hex, [sha1_hex, ...])
//    returns the sha1 of the file if it matches any of the hex
//    strings passed, or "" if it does not equal any of them.
//
Value* Sha1CheckFn(const char* name, State* state, int argc, Expr* argv[]) {
    if (argc < 1) {
        return ErrorAbort(state, "%s() expects at least 1 arg", name);
    }

    Value** args = ReadValueVarArgs(state, argc, argv);
    if (args == NULL) {
        return NULL;
    }

    if (args[0]->size < 0) {
        fprintf(stderr, "%s(): no file contents received", name);
        return StringValue(strdup(""));
    }
    uint8_t digest[SHA_DIGEST_SIZE];
    SHA(args[0]->data, args[0]->size, digest);
    FreeValue(args[0]);

    if (argc == 1) {
        return StringValue(PrintSha1(digest));
    }

    int i;
    uint8_t* arg_digest = malloc(SHA_DIGEST_SIZE);
    for (i = 1; i < argc; ++i) {
        if (args[i]->type != VAL_STRING) {
            fprintf(stderr, "%s(): arg %d is not a string; skipping",
                    name, i);
        } else if (ParseSha1(args[i]->data, arg_digest) != 0) {
            // Warn about bad args and skip them.
            fprintf(stderr, "%s(): error parsing \"%s\" as sha-1; skipping",
                    name, args[i]->data);
        } else if (memcmp(digest, arg_digest, SHA_DIGEST_SIZE) == 0) {
            break;
        }
        FreeValue(args[i]);
    }
    if (i >= argc) {
        // Didn't match any of the hex strings; return false.
        return StringValue(strdup(""));
    }
    // Found a match; free all the remaining arguments and return the
    // matched one.
    int j;
    for (j = i+1; j < argc; ++j) {
        FreeValue(args[j]);
    }
    return args[i];
}

// Read a local file and return its contents (the char* returned
// is actually a FileContents*).
Value* ReadFileFn(const char* name, State* state, int argc, Expr* argv[]) {
    if (argc != 1) {
        return ErrorAbort(state, "%s() expects 1 arg, got %d", name, argc);
    }
    char* filename;
    if (ReadArgs(state, argv, 1, &filename) < 0) return NULL;

    Value* v = malloc(sizeof(Value));
    v->type = VAL_BLOB;

    FileContents fc;
    if (LoadFileContents(filename, &fc) != 0) {
        ErrorAbort(state, "%s() loading \"%s\" failed: %s",
                   name, filename, strerror(errno));
        free(filename);
        free(v);
        free(fc.data);
        return NULL;
    }

    v->size = fc.size;
    v->data = (char*)fc.data;

    free(filename);
    return v;
}

void RegisterInstallFunctions() {
    RegisterFunction("mount", MountFn);
    RegisterFunction("is_mounted", IsMountedFn);
    RegisterFunction("unmount", UnmountFn);
    RegisterFunction("format", FormatFn);
    RegisterFunction("show_progress", ShowProgressFn);
    RegisterFunction("set_progress", SetProgressFn);
    RegisterFunction("delete", DeleteFn);
    RegisterFunction("delete_recursive", DeleteFn);
    RegisterFunction("package_extract_dir", PackageExtractDirFn);
    RegisterFunction("package_extract_file", PackageExtractFileFn);
    RegisterFunction("symlink", SymlinkFn);
    RegisterFunction("set_perm", SetPermFn);
    RegisterFunction("set_perm_recursive", SetPermFn);

    RegisterFunction("getprop", GetPropFn);
    RegisterFunction("file_getprop", FileGetPropFn);
    RegisterFunction("write_raw_image", WriteRawImageFn);

    RegisterFunction("apply_patch", ApplyPatchFn);
    RegisterFunction("apply_patch_check", ApplyPatchCheckFn);
    RegisterFunction("apply_patch_space", ApplyPatchSpaceFn);

    RegisterFunction("read_file", ReadFileFn);
    RegisterFunction("sha1_check", Sha1CheckFn);

    RegisterFunction("ui_print", UIPrintFn);

    RegisterFunction("run_program", RunProgramFn);
}