diff --git a/applypatch/imgpatch.c b/applypatch/imgpatch.c
index 5322817..e3ee80a 100644
--- a/applypatch/imgpatch.c
+++ b/applypatch/imgpatch.c
@@ -36,329 +36,184 @@
  * Return 0 on success.
  */
 int ApplyImagePatch(const unsigned char* old_data, ssize_t old_size,
-                    const char* patch_filename,
+                    const Value* patch,
                     SinkFn sink, void* token, SHA_CTX* ctx) {
-  FILE* f;
-  if ((f = fopen(patch_filename, "rb")) == NULL) {
-    printf("failed to open patch file\n");
-    return -1;
-  }
-
-  unsigned char header[12];
-  if (fread(header, 1, 12, f) != 12) {
-    printf("failed to read patch file header\n");
-    return -1;
-  }
-
-  // IMGDIFF1 uses CHUNK_NORMAL and CHUNK_GZIP.
-  // IMGDIFF2 uses CHUNK_NORMAL, CHUNK_DEFLATE, and CHUNK_RAW.
-  if (memcmp(header, "IMGDIFF", 7) != 0 ||
-      (header[7] != '1' && header[7] != '2')) {
-    printf("corrupt patch file header (magic number)\n");
-    return -1;
-  }
-
-  int num_chunks = Read4(header+8);
-
-  int i;
-  for (i = 0; i < num_chunks; ++i) {
-    // each chunk's header record starts with 4 bytes.
-    unsigned char chunk[4];
-    if (fread(chunk, 1, 4, f) != 4) {
-      printf("failed to read chunk %d record\n", i);
-      return -1;
+    ssize_t pos = 12;
+    char* header = patch->data;
+    if (patch->size < 12) {
+        printf("patch too short to contain header\n");
+        return -1;
     }
 
-    int type = Read4(chunk);
-
-    if (type == CHUNK_NORMAL) {
-      unsigned char normal_header[24];
-      if (fread(normal_header, 1, 24, f) != 24) {
-        printf("failed to read chunk %d normal header data\n", i);
+    // IMGDIFF2 uses CHUNK_NORMAL, CHUNK_DEFLATE, and CHUNK_RAW.
+    // (IMGDIFF1, which is no longer supported, used CHUNK_NORMAL and
+    // CHUNK_GZIP.)
+    if (memcmp(header, "IMGDIFF2", 8) != 0) {
+        printf("corrupt patch file header (magic number)\n");
         return -1;
-      }
-
-      size_t src_start = Read8(normal_header);
-      size_t src_len = Read8(normal_header+8);
-      size_t patch_offset = Read8(normal_header+16);
-
-      printf("CHUNK %d:  normal   patch offset %d\n", i, patch_offset);
-
-      ApplyBSDiffPatch(old_data + src_start, src_len,
-                       patch_filename, patch_offset,
-                       sink, token, ctx);
-    } else if (type == CHUNK_GZIP) {
-      // This branch is basically a duplicate of the CHUNK_DEFLATE
-      // branch, with a bit of extra processing for the gzip header
-      // and footer.  I've avoided factoring the common code out since
-      // this branch will just be deleted when we drop support for
-      // IMGDIFF1.
-
-      // gzip chunks have an additional 64 + gzip_header_len + 8 bytes
-      // in their chunk header.
-      unsigned char* gzip = malloc(64);
-      if (fread(gzip, 1, 64, f) != 64) {
-        printf("failed to read chunk %d initial gzip header data\n",
-                i);
-        return -1;
-      }
-      size_t gzip_header_len = Read4(gzip+60);
-      gzip = realloc(gzip, 64 + gzip_header_len + 8);
-      if (fread(gzip+64, 1, gzip_header_len+8, f) != gzip_header_len+8) {
-        printf("failed to read chunk %d remaining gzip header data\n",
-                i);
-        return -1;
-      }
-
-      size_t src_start = Read8(gzip);
-      size_t src_len = Read8(gzip+8);
-      size_t patch_offset = Read8(gzip+16);
-
-      size_t expanded_len = Read8(gzip+24);
-      size_t target_len = Read8(gzip+32);
-      int gz_level = Read4(gzip+40);
-      int gz_method = Read4(gzip+44);
-      int gz_windowBits = Read4(gzip+48);
-      int gz_memLevel = Read4(gzip+52);
-      int gz_strategy = Read4(gzip+56);
-
-      printf("CHUNK %d:  gzip     patch offset %d\n", i, patch_offset);
-
-      // Decompress the source data; the chunk header tells us exactly
-      // how big we expect it to be when decompressed.
-
-      unsigned char* expanded_source = malloc(expanded_len);
-      if (expanded_source == NULL) {
-        printf("failed to allocate %d bytes for expanded_source\n",
-                expanded_len);
-        return -1;
-      }
-
-      z_stream strm;
-      strm.zalloc = Z_NULL;
-      strm.zfree = Z_NULL;
-      strm.opaque = Z_NULL;
-      strm.avail_in = src_len - (gzip_header_len + 8);
-      strm.next_in = (unsigned char*)(old_data + src_start + gzip_header_len);
-      strm.avail_out = expanded_len;
-      strm.next_out = expanded_source;
-
-      int ret;
-      ret = inflateInit2(&strm, -15);
-      if (ret != Z_OK) {
-        printf("failed to init source inflation: %d\n", ret);
-        return -1;
-      }
-
-      // Because we've provided enough room to accommodate the output
-      // data, we expect one call to inflate() to suffice.
-      ret = inflate(&strm, Z_SYNC_FLUSH);
-      if (ret != Z_STREAM_END) {
-        printf("source inflation returned %d\n", ret);
-        return -1;
-      }
-      // We should have filled the output buffer exactly.
-      if (strm.avail_out != 0) {
-        printf("source inflation short by %d bytes\n", strm.avail_out);
-        return -1;
-      }
-      inflateEnd(&strm);
-
-      // Next, apply the bsdiff patch (in memory) to the uncompressed
-      // data.
-      unsigned char* uncompressed_target_data;
-      ssize_t uncompressed_target_size;
-      if (ApplyBSDiffPatchMem(expanded_source, expanded_len,
-                              patch_filename, patch_offset,
-                              &uncompressed_target_data,
-                              &uncompressed_target_size) != 0) {
-        return -1;
-      }
-
-      // Now compress the target data and append it to the output.
-
-      // start with the gzip header.
-      sink(gzip+64, gzip_header_len, token);
-      SHA_update(ctx, gzip+64, gzip_header_len);
-
-      // we're done with the expanded_source data buffer, so we'll
-      // reuse that memory to receive the output of deflate.
-      unsigned char* temp_data = expanded_source;
-      ssize_t temp_size = expanded_len;
-      if (temp_size < 32768) {
-        // ... unless the buffer is too small, in which case we'll
-        // allocate a fresh one.
-        free(temp_data);
-        temp_data = malloc(32768);
-        temp_size = 32768;
-      }
-
-      // now the deflate stream
-      strm.zalloc = Z_NULL;
-      strm.zfree = Z_NULL;
-      strm.opaque = Z_NULL;
-      strm.avail_in = uncompressed_target_size;
-      strm.next_in = uncompressed_target_data;
-      ret = deflateInit2(&strm, gz_level, gz_method, gz_windowBits,
-                         gz_memLevel, gz_strategy);
-      do {
-        strm.avail_out = temp_size;
-        strm.next_out = temp_data;
-        ret = deflate(&strm, Z_FINISH);
-        size_t have = temp_size - strm.avail_out;
-
-        if (sink(temp_data, have, token) != have) {
-          printf("failed to write %d compressed bytes to output\n",
-                  have);
-          return -1;
-        }
-        SHA_update(ctx, temp_data, have);
-      } while (ret != Z_STREAM_END);
-      deflateEnd(&strm);
-
-      // lastly, the gzip footer.
-      sink(gzip+64+gzip_header_len, 8, token);
-      SHA_update(ctx, gzip+64+gzip_header_len, 8);
-
-      free(temp_data);
-      free(uncompressed_target_data);
-      free(gzip);
-    } else if (type == CHUNK_RAW) {
-      unsigned char raw_header[4];
-      if (fread(raw_header, 1, 4, f) != 4) {
-        printf("failed to read chunk %d raw header data\n", i);
-        return -1;
-      }
-
-      size_t data_len = Read4(raw_header);
-
-      printf("CHUNK %d:  raw      data %d\n", i, data_len);
-
-      unsigned char* temp = malloc(data_len);
-      if (fread(temp, 1, data_len, f) != data_len) {
-          printf("failed to read chunk %d raw data\n", i);
-          return -1;
-      }
-      SHA_update(ctx, temp, data_len);
-      if (sink(temp, data_len, token) != data_len) {
-          printf("failed to write chunk %d raw data\n", i);
-          return -1;
-      }
-    } else if (type == CHUNK_DEFLATE) {
-      // deflate chunks have an additional 60 bytes in their chunk header.
-      unsigned char deflate_header[60];
-      if (fread(deflate_header, 1, 60, f) != 60) {
-        printf("failed to read chunk %d deflate header data\n", i);
-        return -1;
-      }
-
-      size_t src_start = Read8(deflate_header);
-      size_t src_len = Read8(deflate_header+8);
-      size_t patch_offset = Read8(deflate_header+16);
-      size_t expanded_len = Read8(deflate_header+24);
-      size_t target_len = Read8(deflate_header+32);
-      int level = Read4(deflate_header+40);
-      int method = Read4(deflate_header+44);
-      int windowBits = Read4(deflate_header+48);
-      int memLevel = Read4(deflate_header+52);
-      int strategy = Read4(deflate_header+56);
-
-      printf("CHUNK %d:  deflate  patch offset %d\n", i, patch_offset);
-
-      // Decompress the source data; the chunk header tells us exactly
-      // how big we expect it to be when decompressed.
-
-      unsigned char* expanded_source = malloc(expanded_len);
-      if (expanded_source == NULL) {
-        printf("failed to allocate %d bytes for expanded_source\n",
-                expanded_len);
-        return -1;
-      }
-
-      z_stream strm;
-      strm.zalloc = Z_NULL;
-      strm.zfree = Z_NULL;
-      strm.opaque = Z_NULL;
-      strm.avail_in = src_len;
-      strm.next_in = (unsigned char*)(old_data + src_start);
-      strm.avail_out = expanded_len;
-      strm.next_out = expanded_source;
-
-      int ret;
-      ret = inflateInit2(&strm, -15);
-      if (ret != Z_OK) {
-        printf("failed to init source inflation: %d\n", ret);
-        return -1;
-      }
-
-      // Because we've provided enough room to accommodate the output
-      // data, we expect one call to inflate() to suffice.
-      ret = inflate(&strm, Z_SYNC_FLUSH);
-      if (ret != Z_STREAM_END) {
-        printf("source inflation returned %d\n", ret);
-        return -1;
-      }
-      // We should have filled the output buffer exactly.
-      if (strm.avail_out != 0) {
-        printf("source inflation short by %d bytes\n", strm.avail_out);
-        return -1;
-      }
-      inflateEnd(&strm);
-
-      // Next, apply the bsdiff patch (in memory) to the uncompressed
-      // data.
-      unsigned char* uncompressed_target_data;
-      ssize_t uncompressed_target_size;
-      if (ApplyBSDiffPatchMem(expanded_source, expanded_len,
-                              patch_filename, patch_offset,
-                              &uncompressed_target_data,
-                              &uncompressed_target_size) != 0) {
-        return -1;
-      }
-
-      // Now compress the target data and append it to the output.
-
-      // we're done with the expanded_source data buffer, so we'll
-      // reuse that memory to receive the output of deflate.
-      unsigned char* temp_data = expanded_source;
-      ssize_t temp_size = expanded_len;
-      if (temp_size < 32768) {
-        // ... unless the buffer is too small, in which case we'll
-        // allocate a fresh one.
-        free(temp_data);
-        temp_data = malloc(32768);
-        temp_size = 32768;
-      }
-
-      // now the deflate stream
-      strm.zalloc = Z_NULL;
-      strm.zfree = Z_NULL;
-      strm.opaque = Z_NULL;
-      strm.avail_in = uncompressed_target_size;
-      strm.next_in = uncompressed_target_data;
-      ret = deflateInit2(&strm, level, method, windowBits, memLevel, strategy);
-      do {
-        strm.avail_out = temp_size;
-        strm.next_out = temp_data;
-        ret = deflate(&strm, Z_FINISH);
-        size_t have = temp_size - strm.avail_out;
-
-        if (sink(temp_data, have, token) != have) {
-          printf("failed to write %d compressed bytes to output\n",
-                  have);
-          return -1;
-        }
-        SHA_update(ctx, temp_data, have);
-      } while (ret != Z_STREAM_END);
-      deflateEnd(&strm);
-
-      free(temp_data);
-      free(uncompressed_target_data);
-    } else {
-      printf("patch chunk %d is unknown type %d\n", i, type);
-      return -1;
     }
-  }
 
-  return 0;
+    int num_chunks = Read4(header+8);
+
+    int i;
+    for (i = 0; i < num_chunks; ++i) {
+        // each chunk's header record starts with 4 bytes.
+        if (pos + 4 > patch->size) {
+            printf("failed to read chunk %d record\n", i);
+            return -1;
+        }
+        int type = Read4(patch->data + pos);
+        pos += 4;
+
+        if (type == CHUNK_NORMAL) {
+            char* normal_header = patch->data + pos;
+            pos += 24;
+            if (pos > patch->size) {
+                printf("failed to read chunk %d normal header data\n", i);
+                return -1;
+            }
+
+            size_t src_start = Read8(normal_header);
+            size_t src_len = Read8(normal_header+8);
+            size_t patch_offset = Read8(normal_header+16);
+
+            ApplyBSDiffPatch(old_data + src_start, src_len,
+                             patch, patch_offset, sink, token, ctx);
+        } else if (type == CHUNK_RAW) {
+            char* raw_header = patch->data + pos;
+            pos += 4;
+            if (pos > patch->size) {
+                printf("failed to read chunk %d raw header data\n", i);
+                return -1;
+            }
+
+            ssize_t data_len = Read4(raw_header);
+
+            if (pos + data_len > patch->size) {
+                printf("failed to read chunk %d raw data\n", i);
+                return -1;
+            }
+            SHA_update(ctx, patch->data + pos, data_len);
+            if (sink((unsigned char*)patch->data + pos,
+                     data_len, token) != data_len) {
+                printf("failed to write chunk %d raw data\n", i);
+                return -1;
+            }
+            pos += data_len;
+        } else if (type == CHUNK_DEFLATE) {
+            // deflate chunks have an additional 60 bytes in their chunk header.
+            char* deflate_header = patch->data + pos;
+            pos += 60;
+            if (pos > patch->size) {
+                printf("failed to read chunk %d deflate header data\n", i);
+                return -1;
+            }
+
+            size_t src_start = Read8(deflate_header);
+            size_t src_len = Read8(deflate_header+8);
+            size_t patch_offset = Read8(deflate_header+16);
+            size_t expanded_len = Read8(deflate_header+24);
+            size_t target_len = Read8(deflate_header+32);
+            int level = Read4(deflate_header+40);
+            int method = Read4(deflate_header+44);
+            int windowBits = Read4(deflate_header+48);
+            int memLevel = Read4(deflate_header+52);
+            int strategy = Read4(deflate_header+56);
+
+            // Decompress the source data; the chunk header tells us exactly
+            // how big we expect it to be when decompressed.
+
+            unsigned char* expanded_source = malloc(expanded_len);
+            if (expanded_source == NULL) {
+                printf("failed to allocate %d bytes for expanded_source\n",
+                       expanded_len);
+                return -1;
+            }
+
+            z_stream strm;
+            strm.zalloc = Z_NULL;
+            strm.zfree = Z_NULL;
+            strm.opaque = Z_NULL;
+            strm.avail_in = src_len;
+            strm.next_in = (unsigned char*)(old_data + src_start);
+            strm.avail_out = expanded_len;
+            strm.next_out = expanded_source;
+
+            int ret;
+            ret = inflateInit2(&strm, -15);
+            if (ret != Z_OK) {
+                printf("failed to init source inflation: %d\n", ret);
+                return -1;
+            }
+
+            // Because we've provided enough room to accommodate the output
+            // data, we expect one call to inflate() to suffice.
+            ret = inflate(&strm, Z_SYNC_FLUSH);
+            if (ret != Z_STREAM_END) {
+                printf("source inflation returned %d\n", ret);
+                return -1;
+            }
+            // We should have filled the output buffer exactly.
+            if (strm.avail_out != 0) {
+                printf("source inflation short by %d bytes\n", strm.avail_out);
+                return -1;
+            }
+            inflateEnd(&strm);
+
+            // Next, apply the bsdiff patch (in memory) to the uncompressed
+            // data.
+            unsigned char* uncompressed_target_data;
+            ssize_t uncompressed_target_size;
+            if (ApplyBSDiffPatchMem(expanded_source, expanded_len,
+                                    patch, patch_offset,
+                                    &uncompressed_target_data,
+                                    &uncompressed_target_size) != 0) {
+                return -1;
+            }
+
+            // Now compress the target data and append it to the output.
+
+            // we're done with the expanded_source data buffer, so we'll
+            // reuse that memory to receive the output of deflate.
+            unsigned char* temp_data = expanded_source;
+            ssize_t temp_size = expanded_len;
+            if (temp_size < 32768) {
+                // ... unless the buffer is too small, in which case we'll
+                // allocate a fresh one.
+                free(temp_data);
+                temp_data = malloc(32768);
+                temp_size = 32768;
+            }
+
+            // now the deflate stream
+            strm.zalloc = Z_NULL;
+            strm.zfree = Z_NULL;
+            strm.opaque = Z_NULL;
+            strm.avail_in = uncompressed_target_size;
+            strm.next_in = uncompressed_target_data;
+            ret = deflateInit2(&strm, level, method, windowBits, memLevel, strategy);
+            do {
+                strm.avail_out = temp_size;
+                strm.next_out = temp_data;
+                ret = deflate(&strm, Z_FINISH);
+                ssize_t have = temp_size - strm.avail_out;
+
+                if (sink(temp_data, have, token) != have) {
+                    printf("failed to write %ld compressed bytes to output\n",
+                           (long)have);
+                    return -1;
+                }
+                SHA_update(ctx, temp_data, have);
+            } while (ret != Z_STREAM_END);
+            deflateEnd(&strm);
+
+            free(temp_data);
+            free(uncompressed_target_data);
+        } else {
+            printf("patch chunk %d is unknown type %d\n", i, type);
+            return -1;
+        }
+    }
+
+    return 0;
 }