Add magic_number_guess_fourcc prefix_closed arg
diff --git a/example/convert-to-nia/convert-to-nia.c b/example/convert-to-nia/convert-to-nia.c
index 76eeb3c..2c52b88 100644
--- a/example/convert-to-nia/convert-to-nia.c
+++ b/example/convert-to-nia/convert-to-nia.c
@@ -246,7 +246,7 @@
g_fourcc = 0;
while (true) {
g_fourcc = wuffs_base__magic_number_guess_fourcc(
- wuffs_base__io_buffer__reader_slice(&g_src));
+ wuffs_base__io_buffer__reader_slice(&g_src), g_src.meta.closed);
if ((g_fourcc >= 0) ||
(wuffs_base__io_buffer__reader_length(&g_src) == g_src.data.len)) {
break;
diff --git a/internal/cgen/auxiliary/image.cc b/internal/cgen/auxiliary/image.cc
index 312ec81..0c1b17e 100644
--- a/internal/cgen/auxiliary/image.cc
+++ b/internal/cgen/auxiliary/image.cc
@@ -58,7 +58,8 @@
wuffs_base__image_decoder::unique_ptr //
DecodeImageCallbacks::SelectDecoder(uint32_t fourcc,
- wuffs_base__slice_u8 prefix) {
+ wuffs_base__slice_u8 prefix_data,
+ bool prefix_closed) {
switch (fourcc) {
#if !defined(WUFFS_CONFIG__MODULES) || defined(WUFFS_CONFIG__MODULE__BMP)
case WUFFS_BASE__FOURCC__BMP:
@@ -311,10 +312,17 @@
// Determine the image format.
if (!redirected) {
while (true) {
- fourcc = wuffs_base__magic_number_guess_fourcc(io_buf.reader_slice());
+ fourcc = wuffs_base__magic_number_guess_fourcc(io_buf.reader_slice(),
+ io_buf.meta.closed);
if (fourcc > 0) {
break;
} else if ((fourcc == 0) && (io_buf.reader_length() >= 64)) {
+ // Having (fourcc == 0) means that Wuffs' built in MIME sniffer
+ // didn't recognize the image format. Nonetheless, custom callbacks
+ // may still be able to do their own MIME sniffing, for exotic image
+ // types. We try to give them at least 64 bytes of prefix data when
+ // one-shot-calling callbacks.SelectDecoder. There is no mechanism
+ // for the callbacks to request a longer prefix.
break;
} else if (io_buf.meta.closed || (io_buf.writer_length() == 0)) {
fourcc = 0;
@@ -355,8 +363,7 @@
// Select the image decoder.
image_decoder = callbacks.SelectDecoder(
- (uint32_t)fourcc,
- fourcc ? wuffs_base__empty_slice_u8() : io_buf.reader_slice());
+ (uint32_t)fourcc, io_buf.reader_slice(), io_buf.meta.closed);
if (!image_decoder) {
return DecodeImageResult(DecodeImage_UnsupportedImageFormat);
}
diff --git a/internal/cgen/auxiliary/image.hh b/internal/cgen/auxiliary/image.hh
index 96919a5..a3dd0f5 100644
--- a/internal/cgen/auxiliary/image.hh
+++ b/internal/cgen/auxiliary/image.hh
@@ -70,9 +70,13 @@
// Returning a nullptr means failure (DecodeImage_UnsupportedImageFormat).
//
// Common formats will have a FourCC value in the range [1 ..= 0x7FFF_FFFF],
- // such as WUFFS_BASE__FOURCC__JPEG. A zero FourCC value means that the
- // caller is responsible for examining the opening bytes (a prefix) of the
- // input data. SelectDecoder implementations should not modify those bytes.
+ // such as WUFFS_BASE__FOURCC__JPEG. A zero FourCC value means that Wuffs'
+ // standard library did not recognize the image format but if SelectDecoder
+ // was overridden, it may examine the input data's starting bytes and still
+ // provide its own image decoder, e.g. for an exotic image file format that's
+ // not in Wuffs' standard library. The prefix_etc fields have the same
+ // meaning as wuffs_base__magic_number_guess_fourcc arguments. SelectDecoder
+ // implementations should not modify prefix_data's contents.
//
// SelectDecoder might be called more than once, since some image file
// formats can wrap others. For example, a nominal BMP file can actually
@@ -89,7 +93,9 @@
// - WUFFS_BASE__FOURCC__PNG
// - WUFFS_BASE__FOURCC__WBMP
virtual wuffs_base__image_decoder::unique_ptr //
- SelectDecoder(uint32_t fourcc, wuffs_base__slice_u8 prefix);
+ SelectDecoder(uint32_t fourcc,
+ wuffs_base__slice_u8 prefix_data,
+ bool prefix_closed);
// HandleMetadata acknowledges image metadata. minfo.flavor will be one of:
// - WUFFS_BASE__MORE_INFORMATION__FLAVOR__METADATA_RAW_PASSTHROUGH
diff --git a/internal/cgen/base/fundamental-public.h b/internal/cgen/base/fundamental-public.h
index 43ead3f..b4af4de 100644
--- a/internal/cgen/base/fundamental-public.h
+++ b/internal/cgen/base/fundamental-public.h
@@ -1418,13 +1418,19 @@
// ---------------- Magic Numbers
// wuffs_base__magic_number_guess_fourcc guesses the file format of some data,
-// given its opening bytes. It returns a positive FourCC value on success.
+// given its starting bytes (the prefix_data argument) and whether or not there
+// may be further bytes (the prefix_closed argument; true means that
+// prefix_data is the entire data).
+//
+// It returns a positive FourCC value on success.
//
// It returns zero if nothing matches its hard-coded list of 'magic numbers'.
//
-// It returns a negative value if a longer prefix is required for a conclusive
-// result. For example, seeing a single 'B' byte is not enough to discriminate
-// the BMP and BPG image file formats.
+// It returns a negative value if prefix_closed is false and a longer prefix is
+// required for a conclusive result. For example, a single 'B' byte (without
+// further data) is not enough to discriminate the BMP and BPG image file
+// formats. Similarly, a single '\xFF' byte might be the start of JPEG data or
+// it might be the start of some other binary data.
//
// It does not do a full validity check. Like any guess made from a short
// prefix of the data, it may return false positives. Data that starts with 99
@@ -1439,4 +1445,5 @@
// function requires the WUFFS_CONFIG__MODULE__BASE__MAGIC sub-module, not just
// WUFFS_CONFIG__MODULE__BASE__CORE.
WUFFS_BASE__MAYBE_STATIC int32_t //
-wuffs_base__magic_number_guess_fourcc(wuffs_base__slice_u8 prefix);
+wuffs_base__magic_number_guess_fourcc(wuffs_base__slice_u8 prefix_data,
+ bool prefix_closed);
diff --git a/internal/cgen/base/magic-submodule.c b/internal/cgen/base/magic-submodule.c
index beb3e8a..cf35c4d 100644
--- a/internal/cgen/base/magic-submodule.c
+++ b/internal/cgen/base/magic-submodule.c
@@ -23,7 +23,8 @@
// See:
// - https://docs.fileformat.com/image/ico/
static int32_t //
-wuffs_base__magic_number_guess_fourcc__maybe_ico(wuffs_base__slice_u8 prefix) {
+wuffs_base__magic_number_guess_fourcc__maybe_ico(wuffs_base__slice_u8 prefix,
+ bool prefix_closed) {
// Allow-list for the Image Type field.
if (prefix.len < 4) {
return -1;
@@ -66,7 +67,8 @@
// - https://docs.fileformat.com/image/tga/
// - https://www.dca.fee.unicamp.br/~martino/disciplinas/ea978/tgaffs.pdf
static int32_t //
-wuffs_base__magic_number_guess_fourcc__maybe_tga(wuffs_base__slice_u8 prefix) {
+wuffs_base__magic_number_guess_fourcc__maybe_tga(wuffs_base__slice_u8 prefix,
+ bool prefix_closed) {
// Allow-list for the Image Type field.
if (prefix.len < 3) {
return -1;
@@ -120,7 +122,8 @@
}
WUFFS_BASE__MAYBE_STATIC int32_t //
-wuffs_base__magic_number_guess_fourcc(wuffs_base__slice_u8 prefix) {
+wuffs_base__magic_number_guess_fourcc(wuffs_base__slice_u8 prefix,
+ bool prefix_closed) {
// This is similar to (but different from):
// - the magic/Magdir tables under https://github.com/file/file
// - the MIME Sniffing algorithm at https://mimesniff.spec.whatwg.org/
@@ -189,7 +192,8 @@
if (prefix.len < 2) {
return -1;
} else if ((prefix.ptr[1] == 0x00) || (prefix.ptr[1] == 0x01)) {
- return wuffs_base__magic_number_guess_fourcc__maybe_tga(prefix);
+ return wuffs_base__magic_number_guess_fourcc__maybe_tga(prefix,
+ prefix_closed);
}
return 0;
@@ -214,11 +218,13 @@
// identifier, so we have to use heuristics (where the order matters, the
// same as /usr/bin/file's magic/Magdir tables) as best we can. Maybe
// it's TGA, ICO/CUR, etc. Maybe it's something else.
- int32_t tga = wuffs_base__magic_number_guess_fourcc__maybe_tga(prefix);
+ int32_t tga = wuffs_base__magic_number_guess_fourcc__maybe_tga(
+ prefix, prefix_closed);
if (tga != 0) {
return tga;
}
- int32_t ico = wuffs_base__magic_number_guess_fourcc__maybe_ico(prefix);
+ int32_t ico = wuffs_base__magic_number_guess_fourcc__maybe_ico(
+ prefix, prefix_closed);
if (ico != 0) {
return ico;
}
diff --git a/release/c/wuffs-unsupported-snapshot.c b/release/c/wuffs-unsupported-snapshot.c
index 807e238..61711dc 100644
--- a/release/c/wuffs-unsupported-snapshot.c
+++ b/release/c/wuffs-unsupported-snapshot.c
@@ -1685,13 +1685,19 @@
// ---------------- Magic Numbers
// wuffs_base__magic_number_guess_fourcc guesses the file format of some data,
-// given its opening bytes. It returns a positive FourCC value on success.
+// given its starting bytes (the prefix_data argument) and whether or not there
+// may be further bytes (the prefix_closed argument; true means that
+// prefix_data is the entire data).
+//
+// It returns a positive FourCC value on success.
//
// It returns zero if nothing matches its hard-coded list of 'magic numbers'.
//
-// It returns a negative value if a longer prefix is required for a conclusive
-// result. For example, seeing a single 'B' byte is not enough to discriminate
-// the BMP and BPG image file formats.
+// It returns a negative value if prefix_closed is false and a longer prefix is
+// required for a conclusive result. For example, a single 'B' byte (without
+// further data) is not enough to discriminate the BMP and BPG image file
+// formats. Similarly, a single '\xFF' byte might be the start of JPEG data or
+// it might be the start of some other binary data.
//
// It does not do a full validity check. Like any guess made from a short
// prefix of the data, it may return false positives. Data that starts with 99
@@ -1706,7 +1712,8 @@
// function requires the WUFFS_CONFIG__MODULE__BASE__MAGIC sub-module, not just
// WUFFS_CONFIG__MODULE__BASE__CORE.
WUFFS_BASE__MAYBE_STATIC int32_t //
-wuffs_base__magic_number_guess_fourcc(wuffs_base__slice_u8 prefix);
+wuffs_base__magic_number_guess_fourcc(wuffs_base__slice_u8 prefix_data,
+ bool prefix_closed);
// ---------------- Ranges and Rects
@@ -10238,9 +10245,13 @@
// Returning a nullptr means failure (DecodeImage_UnsupportedImageFormat).
//
// Common formats will have a FourCC value in the range [1 ..= 0x7FFF_FFFF],
- // such as WUFFS_BASE__FOURCC__JPEG. A zero FourCC value means that the
- // caller is responsible for examining the opening bytes (a prefix) of the
- // input data. SelectDecoder implementations should not modify those bytes.
+ // such as WUFFS_BASE__FOURCC__JPEG. A zero FourCC value means that Wuffs'
+ // standard library did not recognize the image format but if SelectDecoder
+ // was overridden, it may examine the input data's starting bytes and still
+ // provide its own image decoder, e.g. for an exotic image file format that's
+ // not in Wuffs' standard library. The prefix_etc fields have the same
+ // meaning as wuffs_base__magic_number_guess_fourcc arguments. SelectDecoder
+ // implementations should not modify prefix_data's contents.
//
// SelectDecoder might be called more than once, since some image file
// formats can wrap others. For example, a nominal BMP file can actually
@@ -10257,7 +10268,9 @@
// - WUFFS_BASE__FOURCC__PNG
// - WUFFS_BASE__FOURCC__WBMP
virtual wuffs_base__image_decoder::unique_ptr //
- SelectDecoder(uint32_t fourcc, wuffs_base__slice_u8 prefix);
+ SelectDecoder(uint32_t fourcc,
+ wuffs_base__slice_u8 prefix_data,
+ bool prefix_closed);
// HandleMetadata acknowledges image metadata. minfo.flavor will be one of:
// - WUFFS_BASE__MORE_INFORMATION__FLAVOR__METADATA_RAW_PASSTHROUGH
@@ -15584,7 +15597,8 @@
// See:
// - https://docs.fileformat.com/image/ico/
static int32_t //
-wuffs_base__magic_number_guess_fourcc__maybe_ico(wuffs_base__slice_u8 prefix) {
+wuffs_base__magic_number_guess_fourcc__maybe_ico(wuffs_base__slice_u8 prefix,
+ bool prefix_closed) {
// Allow-list for the Image Type field.
if (prefix.len < 4) {
return -1;
@@ -15627,7 +15641,8 @@
// - https://docs.fileformat.com/image/tga/
// - https://www.dca.fee.unicamp.br/~martino/disciplinas/ea978/tgaffs.pdf
static int32_t //
-wuffs_base__magic_number_guess_fourcc__maybe_tga(wuffs_base__slice_u8 prefix) {
+wuffs_base__magic_number_guess_fourcc__maybe_tga(wuffs_base__slice_u8 prefix,
+ bool prefix_closed) {
// Allow-list for the Image Type field.
if (prefix.len < 3) {
return -1;
@@ -15681,7 +15696,8 @@
}
WUFFS_BASE__MAYBE_STATIC int32_t //
-wuffs_base__magic_number_guess_fourcc(wuffs_base__slice_u8 prefix) {
+wuffs_base__magic_number_guess_fourcc(wuffs_base__slice_u8 prefix,
+ bool prefix_closed) {
// This is similar to (but different from):
// - the magic/Magdir tables under https://github.com/file/file
// - the MIME Sniffing algorithm at https://mimesniff.spec.whatwg.org/
@@ -15750,7 +15766,8 @@
if (prefix.len < 2) {
return -1;
} else if ((prefix.ptr[1] == 0x00) || (prefix.ptr[1] == 0x01)) {
- return wuffs_base__magic_number_guess_fourcc__maybe_tga(prefix);
+ return wuffs_base__magic_number_guess_fourcc__maybe_tga(prefix,
+ prefix_closed);
}
return 0;
@@ -15775,11 +15792,13 @@
// identifier, so we have to use heuristics (where the order matters, the
// same as /usr/bin/file's magic/Magdir tables) as best we can. Maybe
// it's TGA, ICO/CUR, etc. Maybe it's something else.
- int32_t tga = wuffs_base__magic_number_guess_fourcc__maybe_tga(prefix);
+ int32_t tga = wuffs_base__magic_number_guess_fourcc__maybe_tga(
+ prefix, prefix_closed);
if (tga != 0) {
return tga;
}
- int32_t ico = wuffs_base__magic_number_guess_fourcc__maybe_ico(prefix);
+ int32_t ico = wuffs_base__magic_number_guess_fourcc__maybe_ico(
+ prefix, prefix_closed);
if (ico != 0) {
return ico;
}
@@ -43055,7 +43074,8 @@
wuffs_base__image_decoder::unique_ptr //
DecodeImageCallbacks::SelectDecoder(uint32_t fourcc,
- wuffs_base__slice_u8 prefix) {
+ wuffs_base__slice_u8 prefix_data,
+ bool prefix_closed) {
switch (fourcc) {
#if !defined(WUFFS_CONFIG__MODULES) || defined(WUFFS_CONFIG__MODULE__BMP)
case WUFFS_BASE__FOURCC__BMP:
@@ -43308,10 +43328,17 @@
// Determine the image format.
if (!redirected) {
while (true) {
- fourcc = wuffs_base__magic_number_guess_fourcc(io_buf.reader_slice());
+ fourcc = wuffs_base__magic_number_guess_fourcc(io_buf.reader_slice(),
+ io_buf.meta.closed);
if (fourcc > 0) {
break;
} else if ((fourcc == 0) && (io_buf.reader_length() >= 64)) {
+ // Having (fourcc == 0) means that Wuffs' built in MIME sniffer
+ // didn't recognize the image format. Nonetheless, custom callbacks
+ // may still be able to do their own MIME sniffing, for exotic image
+ // types. We try to give them at least 64 bytes of prefix data when
+ // one-shot-calling callbacks.SelectDecoder. There is no mechanism
+ // for the callbacks to request a longer prefix.
break;
} else if (io_buf.meta.closed || (io_buf.writer_length() == 0)) {
fourcc = 0;
@@ -43352,8 +43379,7 @@
// Select the image decoder.
image_decoder = callbacks.SelectDecoder(
- (uint32_t)fourcc,
- fourcc ? wuffs_base__empty_slice_u8() : io_buf.reader_slice());
+ (uint32_t)fourcc, io_buf.reader_slice(), io_buf.meta.closed);
if (!image_decoder) {
return DecodeImageResult(DecodeImage_UnsupportedImageFormat);
}
