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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,204 @@ | ||
| export const getPngChunkText = (filedata: string) => { | ||
| const binaryString = atob(filedata) | ||
|
|
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| const bytes = new Uint8Array(binaryString.length).map( | ||
| (item, index) => (item = binaryString.charCodeAt(index)) | ||
| ) | ||
| const chunk = extractChunks(bytes) | ||
| return JSON.parse(atob(decodePNG(chunk).text)) | ||
| } | ||
|
|
||
| /// PNG DATA | ||
|
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||
| function extractChunks(data: Uint8Array) { | ||
| if (data[0] !== 0x89 || data[1] !== 0x50 || data[2] !== 0x4e || data[3] !== 0x47) | ||
| throw new Error('Invalid .png file header') | ||
|
|
||
| if (data[4] !== 0x0d || data[5] !== 0x0a || data[6] !== 0x1a || data[7] !== 0x0a) | ||
| throw new Error( | ||
| 'Invalid .png file header: possibly caused by DOS-Unix line ending conversion?' | ||
| ) | ||
|
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| let idx = 8 | ||
|
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| let firstiter = true | ||
| const uint8 = new Uint8Array(4) | ||
| const int32 = new Int32Array(uint8.buffer) | ||
| const uint32 = new Uint32Array(uint8.buffer) | ||
|
|
||
| while (idx < data.length) { | ||
| uint8[3] = data[idx++] | ||
| uint8[2] = data[idx++] | ||
| uint8[1] = data[idx++] | ||
| uint8[0] = data[idx++] | ||
|
|
||
| const length = uint32[0] + 4 | ||
| const chunk = new Uint8Array(length) | ||
|
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||
| chunk[0] = data[idx++] | ||
| chunk[1] = data[idx++] | ||
| chunk[2] = data[idx++] | ||
| chunk[3] = data[idx++] | ||
|
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||
| // Get the name in ASCII for identification. | ||
|
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| const name = | ||
| String.fromCharCode(chunk[0]) + | ||
| String.fromCharCode(chunk[1]) + | ||
| String.fromCharCode(chunk[2]) + | ||
| String.fromCharCode(chunk[3]) | ||
| // The IHDR header MUST come first. | ||
|
|
||
| if (firstiter && name !== 'IHDR') { | ||
| throw new Error('IHDR header missing') | ||
| } else { | ||
| firstiter = false | ||
| } | ||
| // for cui, we only want the tEXt chunk | ||
| if (name !== 'tEXt') { | ||
| idx += length | ||
| continue | ||
| } | ||
|
|
||
| for (let i = 4; i < length; i++) { | ||
| chunk[i] = data[idx++] | ||
| } | ||
|
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| // Read out the CRC value for comparison. | ||
|
|
||
| // It's stored as an Int32. | ||
|
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| uint8[3] = data[idx++] | ||
| uint8[2] = data[idx++] | ||
| uint8[1] = data[idx++] | ||
| uint8[0] = data[idx++] | ||
|
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| const crcActual = int32[0] | ||
|
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| const crcExpect = crc32_buf(chunk) | ||
| if (crcExpect !== crcActual) { | ||
| throw new Error( | ||
| 'CRC values for ' + name + ' header do not match, PNG file is likely corrupted' | ||
| ) | ||
| } | ||
| // skip the rest of the chunks | ||
| return new Uint8Array(chunk.buffer.slice(4)) | ||
| } | ||
|
|
||
| throw new Error('No tEXt chunk found!') | ||
| } | ||
|
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| function decodePNG(data: Uint8Array) { | ||
| let naming = true | ||
|
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| let text = '' | ||
|
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| let name = '' | ||
|
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| for (let i = 0; i < data.length; i++) { | ||
| const code = data[i] | ||
|
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| if (naming) { | ||
| if (code) { | ||
| name += String.fromCharCode(code) | ||
| } else { | ||
| naming = false | ||
| } | ||
| } else { | ||
| if (code) { | ||
| text += String.fromCharCode(code) | ||
| } else { | ||
| throw new Error( | ||
| 'Invalid NULL character found. 0x00 character is not permitted in tEXt content' | ||
| ) | ||
| } | ||
| } | ||
| } | ||
|
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| return { | ||
| keyword: name, | ||
|
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| text: text, | ||
| } | ||
| } | ||
|
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| function signed_crc_table() { | ||
| let c = 0 | ||
| const table = new Array(256) | ||
|
|
||
| for (let n = 0; n !== 256; ++n) { | ||
| c = n | ||
| c = c & 1 ? -306674912 ^ (c >>> 1) : c >>> 1 | ||
| c = c & 1 ? -306674912 ^ (c >>> 1) : c >>> 1 | ||
| c = c & 1 ? -306674912 ^ (c >>> 1) : c >>> 1 | ||
| c = c & 1 ? -306674912 ^ (c >>> 1) : c >>> 1 | ||
| c = c & 1 ? -306674912 ^ (c >>> 1) : c >>> 1 | ||
| c = c & 1 ? -306674912 ^ (c >>> 1) : c >>> 1 | ||
| c = c & 1 ? -306674912 ^ (c >>> 1) : c >>> 1 | ||
| c = c & 1 ? -306674912 ^ (c >>> 1) : c >>> 1 | ||
| table[n] = c | ||
| } | ||
|
|
||
| return new Int32Array(table) | ||
| } | ||
|
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| const T0 = signed_crc_table() | ||
|
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| function slice_by_16_tables(T: Int32Array) { | ||
| let c = 0, | ||
| v = 0, | ||
| n = 0 | ||
| const table = new Int32Array(4096) | ||
|
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| for (n = 0; n !== 256; ++n) table[n] = T[n] | ||
|
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| for (n = 0; n !== 256; ++n) { | ||
| v = T[n] | ||
|
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| for (c = 256 + n; c < 4096; c += 256) { | ||
| v = (v >>> 8) ^ T[v & 0xff] | ||
| table[c] = v | ||
| } | ||
| } | ||
|
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| const out = [] | ||
|
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| for (n = 1; n !== 16; ++n) out[n - 1] = table.subarray(n * 256, n * 256 + 256) | ||
|
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| return out | ||
| } | ||
|
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| const TT = slice_by_16_tables(T0) | ||
|
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| const [T1, T2, T3, T4, T5, T6, T7, T8, T9, Ta, Tb, Tc, Td, Te, Tf, ..._] = TT | ||
|
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| function crc32_buf(B: Uint8Array) { | ||
| let C = -1, | ||
| L = B.length - 15, | ||
| i = 0 | ||
|
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||
| for (; i < L; ) | ||
| C = | ||
| Tf[B[i++] ^ (C & 255)] ^ | ||
| Te[B[i++] ^ ((C >> 8) & 255)] ^ | ||
| Td[B[i++] ^ ((C >> 16) & 255)] ^ | ||
| Tc[B[i++] ^ (C >>> 24)] ^ | ||
| Tb[B[i++]] ^ | ||
| Ta[B[i++]] ^ | ||
| T9[B[i++]] ^ | ||
| T8[B[i++]] ^ | ||
| T7[B[i++]] ^ | ||
| T6[B[i++]] ^ | ||
| T5[B[i++]] ^ | ||
| T4[B[i++]] ^ | ||
| T3[B[i++]] ^ | ||
| T2[B[i++]] ^ | ||
| T1[B[i++]] ^ | ||
| T0[B[i++]] | ||
|
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| L += 15 | ||
|
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| while (i < L) C = (C >>> 8) ^ T0[(C ^ B[i++]) & 0xff] | ||
|
|
||
| return ~C | ||
| } |
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