[libcamera-devel] [PATCH v3 1/8] android: jpeg: exif: Expand setString to support different encodings

[Laurent Pinchart]

Hi Paul,

Thank you for the patch.

On Sat, Jan 23, 2021 at 02:16:57PM +0900, Paul Elder wrote:
> GPSProcessingMethod and UserComment in EXIF tags can be in UTF-16.
> Expand setString to take an encoding when the field type is undefined.
> Update callers accordingly.
> 
> Signed-off-by: Paul Elder <paul.elder at ideasonboard.com>
> 
> ---
> Changes in v3:
> - use array to contain string encoding codes
> - drop JIS and Undefined
> - clean up setString a bit
> - use the endianness of the exif
> 
> Changes in v2:
> - moved from utils into exif
> - support no-encoding
> ---
>  src/android/jpeg/exif.cpp | 88 +++++++++++++++++++++++++++++++++++----
>  src/android/jpeg/exif.h   | 10 ++++-
>  2 files changed, 89 insertions(+), 9 deletions(-)
> 
> diff --git a/src/android/jpeg/exif.cpp b/src/android/jpeg/exif.cpp
> index 33b3fa7f..5d9492fb 100644
> --- a/src/android/jpeg/exif.cpp
> +++ b/src/android/jpeg/exif.cpp
> @@ -7,6 +7,9 @@
>  
>  #include "exif.h"
>  
> +#include <map>
> +#include <uchar.h>
> +
>  #include "libcamera/internal/log.h"
>  #include "libcamera/internal/utils.h"
>  
> @@ -178,11 +181,18 @@ void Exif::setRational(ExifIfd ifd, ExifTag tag, ExifRational item)
>  	exif_entry_unref(entry);
>  }
>  
> -void Exif::setString(ExifIfd ifd, ExifTag tag, ExifFormat format, const std::string &item)
> +static const std::map<Exif::StringEncoding, std::array<uint8_t, 8>> stringEncodingCodes = {
> +	{ Exif::ASCII,     { 0x41, 0x53, 0x43, 0x49, 0x49, 0x00, 0x00, 0x00 } },
> +	{ Exif::Unicode,   { 0x55, 0x4e, 0x49, 0x43, 0x4f, 0x44, 0x45, 0x00 } },
> +};
> +
> +void Exif::setString(ExifIfd ifd, ExifTag tag, ExifFormat format,
> +		     const std::string &item, StringEncoding encoding)
>  {
>  	std::string ascii;
>  	size_t length;
>  	const char *str;
> +	std::vector<uint8_t> buf;
>  
>  	if (format == EXIF_FORMAT_ASCII) {
>  		ascii = utils::toAscii(item);
> @@ -191,13 +201,47 @@ void Exif::setString(ExifIfd ifd, ExifTag tag, ExifFormat format, const std::str
>  		/* Pad 1 extra byte to null-terminate the ASCII string. */
>  		length = ascii.length() + 1;
>  	} else {
> -		str = item.c_str();
> -
> -		/*
> -		 * Strings stored in different formats (EXIF_FORMAT_UNDEFINED)
> -		 * are not null-terminated.
> -		 */
> -		length = item.length();
> +		std::u16string u16str;
> +
> +		auto encodingString = stringEncodingCodes.find(encoding);
> +		if (encodingString != stringEncodingCodes.end()) {
> +			buf = {
> +				encodingString->second.begin(),
> +				encodingString->second.end()
> +			};
> +		}
> +
> +		switch (encoding) {
> +		case Unicode:
> +			u16str = utf8ToUtf16(item);
> +
> +			buf.resize(8 + u16str.size() * 2);
> +			for (size_t i = 0; i < u16str.size(); i++) {
> +				if (order_ == EXIF_BYTE_ORDER_INTEL) {
> +					buf[8 + 2 * i] = (u16str[i] & 0xff);

You can drop the outer parentheses here and below.

> +					buf[8 + 2 * i + 1] = ((u16str[i] >> 8) & 0xff);
> +				} else {
> +					buf[8 + 2 * i] = ((u16str[i] >> 8) & 0xff);
> +					buf[8 + 2 * i + 1] = (u16str[i] & 0xff);
> +				}
> +			}
> +
> +			str = reinterpret_cast<const char *>(buf.data());
> +			length = buf.size();
> +
> +			break;

Blank line here ?

> +		case ASCII:
> +		case NoEncoding:
> +			buf.insert(buf.end(), item.begin(), item.end());
> +			str = reinterpret_cast<const char *>(buf.data());
> +
> +			/*
> +			 * Strings stored in different formats (EXIF_FORMAT_UNDEFINED)
> +			 * are not null-terminated.
> +			 */
> +			length = buf.size();

The str assignment, comment, and length assignment are common to all
cases, you can move them after th switch.

> +			break;
> +		}
>  	}
>  
>  	ExifEntry *entry = createEntry(ifd, tag, format, length, length);
> @@ -290,6 +334,34 @@ void Exif::setThumbnail(Span<const unsigned char> thumbnail,
>  	setShort(EXIF_IFD_0, EXIF_TAG_COMPRESSION, compression);
>  }
>  
> +/**
> + * \brief Convert UTF-8 string to UTF-16 string
> + * \param[in] str String to convert
> + *
> + * \return \a str in UTF-16
> + */
> +std::u16string Exif::utf8ToUtf16(const std::string &str)
> +{
> +	mbstate_t state{};
> +	char16_t c16;
> +	const char *ptr = str.data();
> +	const char *end = ptr + str.size();
> +
> +	std::u16string ret;
> +	while (size_t rc = mbrtoc16(&c16, ptr, end - ptr + 1, &state)) {
> +		if (rc == static_cast<size_t>(-2) ||
> +		    rc == static_cast<size_t>(-1))
> +			break;
> +
> +		ret.push_back(c16);
> +
> +		if (rc > 0)
> +			ptr += rc;
> +	}
> +
> +	return ret;
> +}
> +
>  [[nodiscard]] int Exif::generate()
>  {
>  	if (exifData_) {
> diff --git a/src/android/jpeg/exif.h b/src/android/jpeg/exif.h
> index 5cab4559..73f231b2 100644
> --- a/src/android/jpeg/exif.h
> +++ b/src/android/jpeg/exif.h
> @@ -26,6 +26,12 @@ public:
>  		JPEG = 6,
>  	};
>  
> +	enum StringEncoding {
> +		NoEncoding = 0,
> +		ASCII = 1,
> +		Unicode = 2,
> +	};
> +
>  	void setMake(const std::string &make);
>  	void setModel(const std::string &model);
>  
> @@ -46,9 +52,11 @@ private:
>  	void setShort(ExifIfd ifd, ExifTag tag, uint16_t item);
>  	void setLong(ExifIfd ifd, ExifTag tag, uint32_t item);
>  	void setString(ExifIfd ifd, ExifTag tag, ExifFormat format,
> -		       const std::string &item);
> +		       const std::string &item, StringEncoding encoding = NoEncoding);

Maybe a line break ?

Those are all minor comments, once addressed,

Reviewed-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>

>  	void setRational(ExifIfd ifd, ExifTag tag, ExifRational item);
>  
> +	std::u16string utf8ToUtf16(const std::string &str);
> +
>  	bool valid_;
>  
>  	ExifData *data_;

-- 
Regards,

Laurent Pinchart