SendMessage uses wrong Accept header

[sappenin]

The IL-RFC-38 specifies that SettlementEngine messages should have an Accept and Content-Type header value of application/octet-stream. However, the current implementation of settlement-core seems to errantly be specifying an Accept header of application/json. The errant code is here.

Here's the error message produced by the settlement-xrp when trying to communicate with the Java Connector:

STDERR: 2020-02-01T20:24:52.986Z settlement-xrp Failed to settle: Error fetching payment details: account=b145eec0-be64-4bb5-b8f5-60deedc2811f xrp=0.000001 Error: socket hang up
STDERR:     at connResetException (internal/errors.js:570:14)
STDERR:     at Socket.socketOnEnd (_http_client.js:440:23)
STDERR:     at Socket.emit (events.js:215:7)
STDERR:     at endReadableNT (_stream_readable.js:1184:12)
STDERR:     at processTicksAndRejections (internal/process/task_queues.js:80:21) {
STDERR:   code: 'ECONNRESET',
STDERR:   config: {
STDERR:     url: 'http://host.testcontainers.internal:8081/accounts/b145eec0-be64-4bb5-b8f5-60deedc2811f/messages',
STDERR:     method: 'post',
STDERR:     data: <Buffer 7b 22 74 79 70 65 22 3a 22 70 61 79 6d 65 6e 74 44 65 74 61 69 6c 73 22 7d>,
STDERR:     headers: {
STDERR:       Accept: 'application/json, text/plain, */*',
STDERR:       'Content-Type': 'application/octet-stream',
STDERR:       'User-Agent': 'axios/0.19.0',
STDERR:       'Content-Length': 25
STDERR:     },
STDERR:     transformRequest: [ [Function: transformRequest] ],
STDERR:     transformResponse: [ [Function: transformResponse] ],
STDERR:     timeout: 10000,
STDERR:     adapter: [Function: httpAdapter],
STDERR:     xsrfCookieName: 'XSRF-TOKEN',
STDERR:     xsrfHeaderName: 'X-XSRF-TOKEN',
STDERR:     maxContentLength: -1,
STDERR:     validateStatus: [Function: validateStatus]
STDERR:   },
STDERR:   request: Writable {
STDERR:     _writableState: WritableState {
STDERR:       objectMode: false,
STDERR:       highWaterMark: 16384,
STDERR:       finalCalled: false,
STDERR:       needDrain: false,
STDERR:       ending: false,
STDERR:       ended: false,
STDERR:       finished: false,
STDERR:       destroyed: false,
STDERR:       decodeStrings: true,
STDERR:       defaultEncoding: 'utf8',
STDERR:       length: 0,
STDERR:       writing: false,
STDERR:       corked: 0,
STDERR:       sync: true,
STDERR:       bufferProcessing: false,
STDERR:       onwrite: [Function: bound onwrite],
STDERR:       writecb: null,
STDERR:       writelen: 0,
STDERR:       bufferedRequest: null,
STDERR:       lastBufferedRequest: null,
STDERR:       pendingcb: 0,
STDERR:       prefinished: false,
STDERR:       errorEmitted: false,
STDERR:       emitClose: true,
STDERR:       autoDestroy: false,
STDERR:       bufferedRequestCount: 0,
STDERR:       corkedRequestsFree: [Object]
STDERR:     },
STDERR:     writable: true,
STDERR:     _events: [Object: null prototype] {
STDERR:       response: [Function: handleResponse],
STDERR:       error: [Function: handleRequestError]
STDERR:     },
STDERR:     _eventsCount: 2,
STDERR:     _maxListeners: undefined,
STDERR:     _options: {
STDERR:       protocol: 'http:',
STDERR:       maxRedirects: 21,
STDERR:       maxBodyLength: 10485760,
STDERR:       path: '/accounts/b145eec0-be64-4bb5-b8f5-60deedc2811f/messages',
STDERR:       method: 'POST',
STDERR:       headers: [Object],
STDERR:       agent: undefined,
STDERR:       auth: undefined,
STDERR:       hostname: 'host.testcontainers.internal',
STDERR:       port: '8081',
STDERR:       nativeProtocols: [Object],
STDERR:       pathname: '/accounts/b145eec0-be64-4bb5-b8f5-60deedc2811f/messages'
STDERR:     },
STDERR:     _redirectCount: 0,
STDERR:     _redirects: [],
STDERR:     _requestBodyLength: 25,
STDERR:     _requestBodyBuffers: [ [Object] ],
STDERR:     _onNativeResponse: [Function],
STDERR:     _currentRequest: ClientRequest {
STDERR:       _events: [Object: null prototype],
STDERR:       _eventsCount: 6,
STDERR:       _maxListeners: undefined,
STDERR:       outputData: [],
STDERR:       outputSize: 0,
STDERR:       writable: true,
STDERR:       _last: true,
STDERR:       chunkedEncoding: false,
STDERR:       shouldKeepAlive: false,
STDERR:       useChunkedEncodingByDefault: true,
STDERR:       sendDate: false,
STDERR:       _removedConnection: false,
STDERR:       _removedContLen: false,
STDERR:       _removedTE: false,
STDERR:       _contentLength: null,
STDERR:       _hasBody: true,
STDERR:       _trailer: '',
STDERR:       finished: true,
STDERR:       _headerSent: true,
STDERR:       socket: [Socket],
STDERR:       connection: [Socket],
STDERR:       _header: 'POST /accounts/b145eec0-be64-4bb5-b8f5-60deedc2811f/messages HTTP/1.1\r\n' +
STDERR:         'Accept: application/json, text/plain, */*\r\n' +
STDERR:         'Content-Type: application/octet-stream\r\n' +
STDERR:         'User-Agent: axios/0.19.0\r\n' +
STDERR:         'Content-Length: 25\r\n' +
STDERR:         'Host: host.testcontainers.internal:8081\r\n' +
STDERR:         'Connection: close\r\n' +
STDERR:         '\r\n',
STDERR:       _onPendingData: [Function: noopPendingOutput],
STDERR:       agent: [Agent],
STDERR:       socketPath: undefined,
STDERR:       method: 'POST',
STDERR:       path: '/accounts/b145eec0-be64-4bb5-b8f5-60deedc2811f/messages',
STDERR:       _ended: false,
STDERR:       res: null,
STDERR:       aborted: false,
STDERR:       timeoutCb: null,
STDERR:       upgradeOrConnect: false,
STDERR:       parser: null,
STDERR:       maxHeadersCount: null,
STDERR:       _redirectable: [Circular],
STDERR:       [Symbol(kNeedDrain)]: false,
STDERR:       [Symbol(isCorked)]: false,
STDERR:       [Symbol(kOutHeaders)]: [Object: null prototype]
STDERR:     },
STDERR:     _currentUrl: 'http://host.testcontainers.internal:8081/accounts/b145eec0-be64-4bb5-b8f5-60deedc2811f/messages'
STDERR:   },
STDERR:   response: undefined,
STDERR:   isAxiosError: true,
STDERR:   toJSON: [Function]
STDERR: }
STDERR: 2020-02-01T20:24:53.003Z settlement-core Settlement completed: leftover=0.0000011 settled=0 amountToSettle=0.0000011 account=b145eec0-be64-4bb5-b8f5-60deedc2811f