移动端个别安装手机图片上传旋转90度 exif.js控制

做微信wap页项目的时候，遇到小米6拍照上传图片旋转的问题，后来查找资料得到

Orientation，进行判断并运用canvas把图片旋转后再上传解决了问题

exif.js读取图像的元数据https://www.cnblogs.com/niuboren/archive/2016/09/19/5883796.html

exif.js

var EXIF = {};
var TiffTags = EXIF.TiffTags = {
    0x0112: "Orientation"
};

function imageHasData(img) {
    return !!(img.exifdata);
}

function getImageData(img, callback) {
    function handleBinaryFile(binFile) {
        var data = findEXIFinJPEG(binFile);
        img.exifdata = data || {};
        if (callback) {
            callback.call(img);
        }
    }

    if (window.FileReader && (img instanceof window.Blob || img instanceof window.File)) {
        var fileReader = new FileReader();
        fileReader.onload = function (e) {
            handleBinaryFile(e.target.result);
        };
        fileReader.readAsArrayBuffer(img);
    }
}

function findEXIFinJPEG(file) {
    var dataView = new DataView(file);

    if ((dataView.getUint8(0) != 0xFF) || (dataView.getUint8(1) != 0xD8)) {
        return false; // not a valid jpeg
    }

    var offset = 2,
        length = file.byteLength,
        marker;

    while (offset < length) {
        if (dataView.getUint8(offset) != 0xFF) {
            return false; // not a valid marker, something is wrong
        }

        marker = dataView.getUint8(offset + 1);

        if (marker == 225) {
            return readEXIFData(dataView, offset + 4, dataView.getUint16(offset + 2) - 2);
        } else {
            offset += 2 + dataView.getUint16(offset + 2);
        }
    }
}

function readTags(file, tiffStart, dirStart, strings, bigEnd) {
    var entries = file.getUint16(dirStart, !bigEnd),
        tags = {},
        entryOffset, tag,
        i;

    for (i = 0; i < entries; i++) {
        entryOffset = dirStart + i * 12 + 2;
        tag = strings[file.getUint16(entryOffset, !bigEnd)];
        tags[tag] = readTagValue(file, entryOffset, tiffStart, dirStart, bigEnd);
    }
    return tags;
}

function readTagValue(file, entryOffset, tiffStart, dirStart, bigEnd) {
    var type = file.getUint16(entryOffset + 2, !bigEnd),
        numValues = file.getUint32(entryOffset + 4, !bigEnd),
        valueOffset = file.getUint32(entryOffset + 8, !bigEnd) + tiffStart,
        offset,
        vals, val, n,
        numerator, denominator;
    switch (type) {
        case 1: // byte, 8-bit unsigned int
        case 7: // undefined, 8-bit byte, value depending on field
            if (numValues == 1) {
                return file.getUint8(entryOffset + 8, !bigEnd);
            } else {
                offset = numValues > 4 ? valueOffset : (entryOffset + 8);
                vals = [];
                for (n = 0; n < numValues; n++) {
                    vals[n] = file.getUint8(offset + n);
                }
                return vals;
            }

        case 2: // ascii, 8-bit byte
            offset = numValues > 4 ? valueOffset : (entryOffset + 8);
            return getStringFromDB(file, offset, numValues - 1);

        case 3: // short, 16 bit int
            if (numValues == 1) {
                return file.getUint16(entryOffset + 8, !bigEnd);
            } else {
                offset = numValues > 2 ? valueOffset : (entryOffset + 8);
                vals = [];
                for (n = 0; n < numValues; n++) {
                    vals[n] = file.getUint16(offset + 2 * n, !bigEnd);
                }
                return vals;
            }

        case 4: // long, 32 bit int
            if (numValues == 1) {
                return file.getUint32(entryOffset + 8, !bigEnd);
            } else {
                vals = [];
                for (n = 0; n < numValues; n++) {
                    vals[n] = file.getUint32(valueOffset + 4 * n, !bigEnd);
                }
                return vals;
            }

        case 5: // rational = two long values, first is numerator, second is denominator
            if (numValues == 1) {
                numerator = file.getUint32(valueOffset, !bigEnd);
                denominator = file.getUint32(valueOffset + 4, !bigEnd);
                val = new Number(numerator / denominator);
                val.numerator = numerator;
                val.denominator = denominator;
                return val;
            } else {
                vals = [];
                for (n = 0; n < numValues; n++) {
                    numerator = file.getUint32(valueOffset + 8 * n, !bigEnd);
                    denominator = file.getUint32(valueOffset + 4 + 8 * n, !bigEnd);
                    vals[n] = new Number(numerator / denominator);
                    vals[n].numerator = numerator;
                    vals[n].denominator = denominator;
                }
                return vals;
            }

        case 9: // slong, 32 bit signed int
            if (numValues == 1) {
                return file.getInt32(entryOffset + 8, !bigEnd);
            } else {
                vals = [];
                for (n = 0; n < numValues; n++) {
                    vals[n] = file.getInt32(valueOffset + 4 * n, !bigEnd);
                }
                return vals;
            }

        case 10: // signed rational, two slongs, first is numerator, second is denominator
            if (numValues == 1) {
                return file.getInt32(valueOffset, !bigEnd) / file.getInt32(valueOffset + 4, !bigEnd);
            } else {
                vals = [];
                for (n = 0; n < numValues; n++) {
                    vals[n] = file.getInt32(valueOffset + 8 * n, !bigEnd) / file.getInt32(valueOffset + 4 + 8 * n, !bigEnd);
                }
                return vals;
            }
    }
}

function getStringFromDB(buffer, start, length) {
    var outstr = "";
    for (n = start; n < start + length; n++) {
        outstr += String.fromCharCode(buffer.getUint8(n));
    }
    return outstr;
}

function readEXIFData(file, start) {
    if (getStringFromDB(file, start, 4) != "Exif") {
        return false;
    }

    var bigEnd,
        tags, tag,
        exifData, gpsData,
        tiffOffset = start + 6;

    // test for TIFF validity and endianness
    if (file.getUint16(tiffOffset) == 0x4949) {
        bigEnd = false;
    } else if (file.getUint16(tiffOffset) == 0x4D4D) {
        bigEnd = true;
    } else {
        return false;
    }

    if (file.getUint16(tiffOffset + 2, !bigEnd) != 0x002A) {
        return false;
    }

    var firstIFDOffset = file.getUint32(tiffOffset + 4, !bigEnd);
    if (firstIFDOffset < 0x00000008) {
        return false;
    }

    tags = readTags(file, tiffOffset, tiffOffset + firstIFDOffset, TiffTags, bigEnd);

    return tags;
}

EXIF.getData = function (img, callback) {
    if ((img instanceof Image || img instanceof HTMLImageElement) && !img.complete) return false;

    if (!imageHasData(img)) {
        getImageData(img, callback);
    } else {
        if (callback) {
            callback.call(img);
        }
    }
    return true;
}

EXIF.getTag = function (img, tag) {
    if (!imageHasData(img)) return;
    return img.exifdata[tag];
}