{"record":{"id":"a881e0da554874c1","repo":"parallax/jsPDF","slug":"unknown-gif-block-0x-buf-p-1-tostring-16","errorCode":null,"errorMessage":"Unknown gif block: 0x\" + buf[p - 1].toString(16)","messagePattern":"Unknown gif block: 0x\" \\+ buf\\[p - 1\\]\\.toString\\(16\\)","errorType":"exception","errorClass":"Error","httpStatus":null,"severity":"error","filePath":"src/libs/omggif.js","lineNumber":591,"sourceCode":"          height: h,\n          has_local_palette: has_local_palette,\n          palette_offset: palette_offset,\n          palette_size: palette_size,\n          data_offset: data_offset,\n          data_length: p - data_offset,\n          transparent_index: transparent_index,\n          interlaced: !!interlace_flag,\n          delay: delay,\n          disposal: disposal\n        });\n        break;\n\n      case 0x3b: // Trailer Marker (end of file).\n        no_eof = false;\n        break;\n\n      default:\n        throw new Error(\"Unknown gif block: 0x\" + buf[p - 1].toString(16));\n        break;\n    }\n  }\n\n  this.numFrames = function() {\n    return frames.length;\n  };\n\n  this.loopCount = function() {\n    return loop_count;\n  };\n\n  this.frameInfo = function(frame_num) {\n    if (frame_num < 0 || frame_num >= frames.length)\n      throw new Error(\"Frame index out of range.\");\n    return frames[frame_num];\n  };\n","sourceCodeStart":573,"sourceCodeEnd":609,"githubUrl":"https://github.com/parallax/jsPDF/blob/a3930ce03a585a26b2c76d12a0f413ce96f6d1a3/src/libs/omggif.js#L573-L609","documentation":"Thrown by the GIF parser's main block loop in GifReader when it reads a block-introducer byte that is not one of the three legal GIF block types (0x21 extension, 0x2c image descriptor, 0x3b trailer). The parser has already passed the GIF87a/89a header check, so this fires when the body stream is corrupt or truncated. omggif uses it as a hard stop because it cannot safely resynchronize on an unknown block.","triggerScenarios":"Passing truncated, corrupted, or non-GIF bytes that happen to start with a valid 'GIF8' header into `new GifReader(buf)`. Also a malformed GIF where an extension sub-block length is wrong, desynchronizing the cursor so the next read lands on a random byte instead of a valid introducer.","commonSituations":"Loading a GIF over HTTP that was cut off mid-transfer; feeding a PNG/JPEG that was mislabeled as GIF but whose early bytes coincidentally matched; passing a Uint8Array whose view is offset or length is wrong; a GIF with a vendor-specific extension the strict parser refuses to skip.","solutions":["Validate the input is a Uint8Array/ArrayBuffer of plausible GIF length and re-fetch the source if it may be truncated.","Wrap `new GifReader(buf)` in try/catch and reject the image / fall back to a placeholder on failure.","If you control the bytes, re-encode the GIF with a mainstream tool (gifsicle/ImageMagick) to strip exotic blocks before embedding in a PDF via jsPDF's processGIF89A.","Confirm the file magic: bytes 0-5 must be 47 49 46 38 (GIF8) before attempting a parse."],"exampleFix":"// before\nvar reader = new GifReader(anyBytes);\nreader.decodeAndBlitFrameRGBA(0, pixels);\n\n// after\nfunction isGif(b) {\n  return b && b.length >= 6 && b[0]===0x47 && b[1]===0x49 && b[2]===0x46 && b[3]===0x38;\n}\nif (!isGif(anyBytes)) throw new Error('not a GIF');\ntry {\n  var reader = new GifReader(anyBytes);\n  reader.decodeAndBlitFrameRGBA(0, pixels);\n} catch (e) {\n  console.warn('GIF parse failed, skipping image', e.message);\n}","handlingStrategy":"validation","validationCode":"function isValidGifBytes(b) {\n  if (!(b instanceof Uint8Array) && !Array.isArray(b)) return false;\n  if (b.length < 13) return false;\n  // GIF8 magic\n  return b[0]===0x47 && b[1]===0x49 && b[2]===0x46 && b[3]===0x38;\n}\nif (!isValidGifBytes(anyBytes)) {\n  throw new Error('Input is not valid GIF data');\n}","typeGuard":"function isGifBytes(b) {\n  return (b instanceof Uint8Array || Array.isArray(b)) &&\n    b.length >= 13 &&\n    b[0]===0x47 && b[1]===0x49 && b[2]===0x46 && b[3]===0x38;\n}","tryCatchPattern":"var reader;\ntry {\n  reader = new GifReader(anyBytes);\n} catch (e) {\n  if (/Unknown gif block/.test(e.message)) {\n    console.warn('Corrupt or unsupported GIF, skipping:', e.message);\n    return null;\n  }\n  throw e;\n}","preventionTips":["Validate the GIF8 magic bytes before constructing a GifReader.","Ensure the byte buffer is complete (not truncated) before parsing.","Re-encode untrusted GIFs with a mainstream library to normalize exotic blocks."],"tags":["gif","parsing","validation","omggif"],"backgroundTag":null,"analyzedSha":"a3930ce03a585a26b2c76d12a0f413ce96f6d1a3","analyzedAt":"2026-08-13T05:33:39.648Z","schemaVersion":2},"datasetVersion":"2026-08-13T09:17:06.757Z"}