2015-07-08

使用 xUtils 上传文件至阿里云 OSS 时遇到的错误

项目中使用 xUtils，在上传 OSS 时遇到问题，参数全都正确，但服务器却返回“400 Bad request”错误。
用 Fiddler 比对正常的请求，发现上传失败时的 RequestBody 中每一项，除了文件 file 以外，都多了 Content-Type: text/plain; charset=UTF-8 和 Content-Transfer-Encoding: 8bit 这两项。
阿里云 OSS 服务端返回的 ErrorCode：400 MalformedPOSTRequest “Post 请求的 body 格式非法”。提示：The body of your POST request is not well-formed multipart/form-data。
文件 file 需要 Content-Type: image/png，至于 Content-Transfer-Encoding: binary 可有可无。

尝试移除上述两个参数后，上传请求被正常接受。
/src/com/lidroid/xutils/http/client/multipart/FormBodyPart.java

package com.lidroid.xutils.http.client.multipart;

import com.lidroid.xutils.http.client.multipart.content.ContentBody;

public class FormBodyPart {

    private final String name;
    private final MinimalFieldHeader header;

    private final ContentBody body;

    public FormBodyPart(final String name, final ContentBody body) {
        super();
        if (name == null) {
            throw new IllegalArgumentException("Name may not be null");
        }
        if (body == null) {
            throw new IllegalArgumentException("Body may not be null");
        }
        this.name = name;
        this.body = body;
        this.header = new MinimalFieldHeader();

        generateContentDisposition(body);
        generateContentType(body);
//        generateTransferEncoding(body); // 改动一：注释掉，不然无法上传到OSS。
    }

    public FormBodyPart(final String name, final ContentBody body, final String contentDisposition) {
        super();
        if (name == null) {
            throw new IllegalArgumentException("Name may not be null");
        }
        if (body == null) {
            throw new IllegalArgumentException("Body may not be null");
        }
        this.name = name;
        this.body = body;
        this.header = new MinimalFieldHeader();

        if (contentDisposition != null) {
            addField(MIME.CONTENT_DISPOSITION, contentDisposition);
        } else {
            generateContentDisposition(body);
        }
        generateContentType(body);
//        generateTransferEncoding(body); // 改动二：注释掉，不然无法上传到OSS。
    }

    public String getName() {
        return this.name;
    }

    public ContentBody getBody() {
        return this.body;
    }

    public MinimalFieldHeader getHeader() {
        return this.header;
    }

    public void addField(final String name, final String value) {
        if (name == null) {
            throw new IllegalArgumentException("Field name may not be null");
        }
        this.header.addField(new MinimalField(name, value));
    }

    protected void generateContentDisposition(final ContentBody body) {
        StringBuilder buffer = new StringBuilder();
        buffer.append("form-data; name=\"");
        buffer.append(getName());
        buffer.append("\"");
        if (body.getFilename() != null) {
            buffer.append("; filename=\"");
            buffer.append(body.getFilename());
            buffer.append("\"");
        }
        addField(MIME.CONTENT_DISPOSITION, buffer.toString());
    }

    protected void generateContentType(final ContentBody body) {
        StringBuilder buffer = new StringBuilder();
        buffer.append(body.getMimeType()); // MimeType cannot be null
        if (body.getCharset() != null) { // charset may legitimately be null
            buffer.append("; charset=");
            buffer.append(body.getCharset());
            return; // 改动三：如果非空就返回，这样file的ContentType任然是保留的。
        }
        addField(MIME.CONTENT_TYPE, buffer.toString());
    }

    protected void generateTransferEncoding(final ContentBody body) {
        addField(MIME.CONTENT_TRANSFER_ENC, body.getTransferEncoding()); // TE cannot be null
    }

}

坑了四个小时。

OSS, Android, xUtils