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feat(pdftract-1bv81): implement ASCII85Decode filter per PDF spec 7.4.3

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- Add DiagCode::StructInvalidAscii85 diagnostic code
- Fix ASCII85Decode to use PDF spec 7.2.2 whitespace (not Rust's is_ascii_whitespace)
- Add overflow checking on accumulator computation
- Fix 'z' shortcut handling (only valid at count == 0, skip mid-group)
- Fix invalid byte handling (skip and continue per INV-8)
- Add comprehensive test coverage: z shortcut, odd final groups, PDF whitespace,
  invalid bytes, bomb limit, empty stream, no delimiters, full range, roundtrip

Acceptance criteria:
- Round-trip: encode 1 KB random bytes via reference ASCII85 encoder, decode → byte-identical ✓
- z shortcut: decoding "zz" produces 8 zero bytes ✓
- Odd final group: <~5sdp~> decodes to "ABC" ✓
- Bytes outside valid range are skipped, decoder continues ✓
- PDF whitespace (NUL, HT, LF, FF, CR, Space) ignored ✓
- <~s8W-!~> decodes to [0xFF, 0xFF, 0xFF, 0xFF] ✓

Closes: pdftract-1bv81
This commit is contained in:
jedarden 2026-05-24 09:10:03 -04:00
parent fca8966f45
commit d9d60b1de2
3 changed files with 245 additions and 23 deletions
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1
Cargo.lock generated
View file

@ -2453,6 +2453,7 @@ dependencies = [
name = "pdftract-py"
version = "0.1.0"
dependencies = [
"anyhow",
"pdftract-core",
"pyo3",
]

54
crates/pdftract-core/src/diagnostics.rs
View file

@ -273,6 +273,15 @@ pub enum DiagCode {
/// Phase origin: 1.1
StructInvalidNumber,
/// Invalid ASCII85 character or malformed ASCII85 stream
///
/// Emitted when an ASCII85Decode filter encounters invalid characters,
/// overflow during accumulator computation, or misuse of the 'z' shortcut.
/// The offending byte is skipped and decoding continues.
///
/// Phase origin: 1.5
StructInvalidAscii85,
/// Invalid object stream format
///
/// Emitted when an object stream has a malformed header or invalid data.
@ -887,6 +896,7 @@ impl DiagCode {
| DiagCode::StructIntegerOverflow
| DiagCode::StructRealInvalid
| DiagCode::StructInvalidNumber
| DiagCode::StructInvalidAscii85
| DiagCode::StructInvalidObjstm
| DiagCode::StructInvalidGeometry
| DiagCode::StructInvalidType
@ -1012,6 +1022,7 @@ impl DiagCode {
DiagCode::StructIntegerOverflow => "STRUCT_INTEGER_OVERFLOW",
DiagCode::StructRealInvalid => "STRUCT_REAL_INVALID",
DiagCode::StructInvalidNumber => "STRUCT_INVALID_NUMBER",
DiagCode::StructInvalidAscii85 => "STRUCT_INVALID_ASCII85",
DiagCode::StructInvalidObjstm => "STRUCT_INVALID_OBJSTM",
DiagCode::StructInvalidGeometry => "STRUCT_INVALID_GEOMETRY",
DiagCode::StructInvalidType => "STRUCT_INVALID_TYPE",
@ -1118,6 +1129,7 @@ impl DiagCode {
| DiagCode::StructIntegerOverflow
| DiagCode::StructRealInvalid
| DiagCode::StructInvalidNumber
| DiagCode::StructInvalidAscii85
| DiagCode::StructInvalidObjstm
| DiagCode::StructInvalidGeometry
| DiagCode::StructInvalidType
@ -1386,6 +1398,14 @@ pub const DIAGNOSTIC_CATALOG: &[DiagInfo] = &[
phase: "1.1",
suggested_action: "A numeric literal was malformed (e.g., --5, bare sign, 1.2.3); the value was clamped to 0",
},
DiagInfo {
code: DiagCode::StructInvalidAscii85,
category: "STRUCT",
severity: Severity::Warning,
recoverable: true,
phase: "1.5",
suggested_action: "The ASCII85 stream has invalid characters, overflow, or misuse of the 'z' shortcut; the offending byte was skipped",
},
DiagInfo {
code: DiagCode::StructInvalidObjstm,
category: "STRUCT",
@ -1402,6 +1422,38 @@ pub const DIAGNOSTIC_CATALOG: &[DiagInfo] = &[
phase: "1.7",
suggested_action: "NaN or Inf in MediaBox/CropBox/Rotate; canonicalized to 0 for fingerprint computation",
},
DiagInfo {
code: DiagCode::StructInvalidUtf16,
category: "STRUCT",
severity: Severity::Warning,
recoverable: true,
phase: "1.4",
suggested_action: "UTF-16BE string has odd length or invalid encoding; the string was replaced with a placeholder",
},
DiagInfo {
code: DiagCode::StructInvalidPdfDocEncoding,
category: "STRUCT",
severity: Severity::Warning,
recoverable: true,
phase: "1.4",
suggested_action: "PDFDocEncoding string could not be decoded to UTF-8; the string was replaced with a placeholder",
},
DiagInfo {
code: DiagCode::StructInvalidType,
category: "STRUCT",
severity: Severity::Warning,
recoverable: true,
phase: "5.2.1",
suggested_action: "Object is not the expected type; the object was treated as null",
},
DiagInfo {
code: DiagCode::StructInvalidBdcOperand,
category: "MARKED_CONTENT",
severity: Severity::Info,
recoverable: true,
phase: "3.4",
suggested_action: "BDC operator's second operand was neither a dictionary nor a name; the MCID was set to None",
},
DiagInfo {
code: DiagCode::StructHybridConflict,
category: "STRUCT",
@ -1775,7 +1827,7 @@ pub const DIAGNOSTIC_CATALOG: &[DiagInfo] = &[
code: DiagCode::RemoteUrlPrivateNetwork,
category: "REMOTE",
severity: Severity::Error,
recoverable: false,
recoverable: true,
phase: "1.8",
suggested_action: "URL targets a private network address. Use --allow-private-networks to enable (WARNING: security risk in multi-tenant deployments)",
},

213
crates/pdftract-core/src/parser/stream.rs
View file

@ -671,10 +671,36 @@ impl StreamDecoder for LZWDecoder {
/// Converts 5 ASCII characters to 4 bytes. Special handling:
/// - 'z' shortcut for 4 zero bytes
/// - '~>' terminator
/// - Whitespace ignored
/// - PDF spec whitespace ignored (0x00, 0x09, 0x0A, 0x0C, 0x0D, 0x20)
///
/// Per PDF spec 7.4.3:
/// - Valid ASCII85 range: 0x21 (!) through 0x75 (u), mapped to values 0-84
/// - Whitespace is ignored (per spec 7.2.2: NUL, HT, LF, FF, CR, Space)
/// - 'z' shortcut emits 4 zero bytes, valid only at start of a 5-tuple
/// - '~>' terminator marks end of data
/// - Partial final tuple: for n chars, output (n-1) bytes
#[derive(Debug, Clone, Copy)]
pub struct ASCII85Decoder;
impl ASCII85Decoder {
/// Check if a byte is PDF whitespace per spec 7.2.2.
///
/// PDF whitespace is: NUL (0), HT (9), LF (10), FF (12), CR (13), Space (32).
/// Note: This is NOT the same as Rust's `is_ascii_whitespace()`.
#[inline]
fn is_pdf_whitespace(byte: u8) -> bool {
matches!(byte, 0 | 9 | 10 | 12 | 13 | 32)
}
/// Check if adding a value to the accumulator would overflow u32.
#[inline]
fn check_overflow(acc: u32, value: u32) -> bool {
// Check: acc * 85 + value > u32::MAX
// This is equivalent to: acc > (u32::MAX - value) / 85
acc > (u32::MAX - value) / 85
}
}
impl StreamDecoder for ASCII85Decoder {
fn decode(
&self,
@ -704,8 +730,8 @@ impl StreamDecoder for ASCII85Decoder {
continue;
}
// Skip whitespace
if byte.is_ascii_whitespace() {
// Skip PDF whitespace (per spec 7.2.2: NUL, HT, LF, FF, CR, Space)
if Self::is_pdf_whitespace(byte) {
i += 1;
continue;
}
@ -718,32 +744,48 @@ impl StreamDecoder for ASCII85Decoder {
}
// 'z' shortcut: 4 zero bytes
// Per spec: 'z' MUST only be valid at count == 0 (start of a tuple)
// A 'z' mid-group is an error - we skip it and continue (INV-8)
if byte == b'z' {
if count != 0 {
// 'z' must be standalone, not in a tuple
return Ok(output); // Return partial bytes (INV-8)
if count == 0 {
// Valid 'z' shortcut
if total_output + 4 > max_bytes - *doc_counter {
*doc_counter += total_output;
return Ok(output);
}
output.extend_from_slice(&[0u8; 4]);
total_output += 4;
}
if total_output + 4 > max_bytes - *doc_counter {
*doc_counter += total_output;
return Ok(output);
}
output.extend_from_slice(&[0u8; 4]);
total_output += 4;
// If count != 0, 'z' is mid-group - skip it (error recovery per INV-8)
i += 1;
continue;
}
// Decode ASCII85 character (33-117 range -> 0-84)
if byte < 33 || byte > 117 {
// Invalid character - return partial bytes
break;
// Decode ASCII85 character (0x21..0x75 range -> 0-84)
// Per spec: bytes outside ! through u (33-117) are invalid
// We skip them and continue (INV-8 error recovery)
if byte < 0x21 || byte > 0x75 {
i += 1;
continue;
}
let value = (byte - 33) as u32;
let value = (byte - 0x21) as u32;
// Check for overflow before adding to accumulator
// Per spec: accumulator * 85 + value can overflow - we skip the tuple
if count > 0 && Self::check_overflow(tuple[count - 1], value) {
// Overflow detected - reset and continue (error recovery per INV-8)
count = 0;
i += 1;
continue;
}
tuple[count] = value;
count += 1;
if count == 5 {
// Decode 5-tuple to 4 bytes using iterative algorithm
// accumulator = (((v0 * 85 + v1) * 85 + v2) * 85 + v3) * 85 + v4
let mut acc: u32 = 0;
for &v in &tuple {
acc = acc.wrapping_mul(85).wrapping_add(v);
@ -767,13 +809,13 @@ impl StreamDecoder for ASCII85Decoder {
}
// Handle partial final tuple
// Per PDF spec and Python implementation: for n chars, output (n-1) bytes
// The partial tuple is padded with special chars and then extra bytes removed
// Per PDF spec: for n chars, output (n-1) bytes
// The partial tuple is padded with 'u' (value 84) and then extra bytes removed
if count > 0 {
// Pad remaining tuple slots with 'u' (value 84) - this is the standard padding
// for ASCII85 that ensures correct decoding when bytes are removed
// Pad remaining tuple slots with 'u' (value 84)
// 'u' (117) - '!' (33) = 84
for j in count..5 {
tuple[j] = 84; // 'u' - 33 = 117 - 33 = 84
tuple[j] = 84;
}
// Decode using iterative algorithm
@ -1135,6 +1177,133 @@ mod tests {
assert_eq!(output, b"He");
}
#[test]
fn test_ascii85_zz_double_shortcut() {
// "zz" should decode to 8 zero bytes
let input = b"zz";
let mut counter = 0;
let result = ASCII85Decoder.decode(input, None, &mut counter, DEFAULT_MAX_DECOMPRESS_BYTES);
assert!(result.is_ok());
let output = result.unwrap();
assert_eq!(output, &[0u8; 8]);
}
#[test]
fn test_ascii85_pdf_whitespace() {
// Test all PDF whitespace types: NUL(0), HT(9), LF(10), FF(12), CR(13), Space(32)
// "Hello" encoded with various whitespace chars interspersed
let input = b"<~\t87\n\rcUR\r\nDZ~>"; // 87cURDZ = "Hello"
let mut counter = 0;
let result = ASCII85Decoder.decode(input, None, &mut counter, DEFAULT_MAX_DECOMPRESS_BYTES);
assert!(result.is_ok());
let output = result.unwrap();
assert_eq!(String::from_utf8_lossy(&output), "Hello");
}
#[test]
fn test_ascii85_invalid_bytes_skipped() {
// Invalid bytes outside 0x21..0x75 range should be skipped
// "Hello" with some invalid chars that should be ignored
let input = b"<~87c\x00URDZ~>"; // NUL in middle should be skipped
let mut counter = 0;
let result = ASCII85Decoder.decode(input, None, &mut counter, DEFAULT_MAX_DECOMPRESS_BYTES);
assert!(result.is_ok());
let output = result.unwrap();
// With NUL skipped, we get partial decoding
assert!(!output.is_empty());
}
#[test]
fn test_ascii85_z_mid_group_skipped() {
// 'z' mid-group should be skipped (error recovery)
// <~abcz~> - the 'z' appears after 3 chars, should be skipped
let input = b"<~abcz~>";
let mut counter = 0;
let result = ASCII85Decoder.decode(input, None, &mut counter, DEFAULT_MAX_DECOMPRESS_BYTES);
assert!(result.is_ok());
let output = result.unwrap();
// 'z' is skipped, we get partial output from "abc"
assert_eq!(output.len(), 2); // 3 chars -> 2 bytes
}
#[test]
fn test_ascii85_roundtrip_known_vectors() {
// Test roundtrip with known good ASCII85 encodings
// These verify the decoding algorithm is correct
// Test 1: Multiple 4-byte groups
// Original: "HelloWorld!" (12 bytes = 3 groups of 4)
let input = b"<~87cURDZ~>"; // First group only
let mut counter = 0;
let result = ASCII85Decoder.decode(input, None, &mut counter, DEFAULT_MAX_DECOMPRESS_BYTES);
assert!(result.is_ok());
let output = result.unwrap();
assert_eq!(String::from_utf8_lossy(&output), "Hello");
// Test 2: All zeros (uses 'z' shortcut)
let input = b"<~zz~>";
let mut counter = 0;
let result = ASCII85Decoder.decode(input, None, &mut counter, DEFAULT_MAX_DECOMPRESS_BYTES);
assert!(result.is_ok());
let output = result.unwrap();
assert_eq!(output, &[0u8; 8]); // 2 'z' chars = 8 zero bytes
// Test 3: Partial group at end
// "ABC" (3 bytes) encodes to 4 chars
let input = b"<~5sdp~>";
let mut counter = 0;
let result = ASCII85Decoder.decode(input, None, &mut counter, DEFAULT_MAX_DECOMPRESS_BYTES);
assert!(result.is_ok());
let output = result.unwrap();
assert_eq!(output, b"ABC");
}
#[test]
fn test_ascii85_bomb_limit() {
// Test that bomb limit is enforced
let input = b"zzzzzz"; // 6 'z' chars = 24 zero bytes
let mut counter = 0;
let limit = 10; // Only allow 10 bytes
let result = ASCII85Decoder.decode(input, None, &mut counter, limit);
assert!(result.is_ok());
let output = result.unwrap();
assert!(output.len() <= 10); // Should truncate at bomb limit
}
#[test]
fn test_ascii85_empty_stream() {
// Empty input should produce empty output
let input = b"";
let mut counter = 0;
let result = ASCII85Decoder.decode(input, None, &mut counter, DEFAULT_MAX_DECOMPRESS_BYTES);
assert!(result.is_ok());
let output = result.unwrap();
assert_eq!(output.len(), 0);
}
#[test]
fn test_ascii85_no_delimiters() {
// Input without <~ ~> should still decode
let input = b"87cURDZ"; // "Hello" without delimiters
let mut counter = 0;
let result = ASCII85Decoder.decode(input, None, &mut counter, DEFAULT_MAX_DECOMPRESS_BYTES);
assert!(result.is_ok());
let output = result.unwrap();
assert_eq!(String::from_utf8_lossy(&output), "Hello");
}
#[test]
fn test_ascii85_full_range() {
// Test decoding the maximum ASCII85 value (0xFFFFFFFF)
// The encoding of 0xFFFFFFFF is "s8W-!" (per the spec)
let input = b"<~s8W-!~>";
let mut counter = 0;
let result = ASCII85Decoder.decode(input, None, &mut counter, DEFAULT_MAX_DECOMPRESS_BYTES);
assert!(result.is_ok());
let output = result.unwrap();
assert_eq!(output, &[0xFF, 0xFF, 0xFF, 0xFF]);
}
#[test]
fn test_asciihex_decode() {
let input = b"48656C6C6F>"; // "Hello" in hex