HttpClient dont return all headers [duplicate]

问题

I'm trying to read some custom headers ("etag") from a httpresponse with angular 6 app:

getProvider(providerName: string, version: string): Observable<any> {
    if (providerName && version) {
        var url = `${this.baseUrl}/v1/config/provider/version/${version}/${providerName}`;
        return this._http.get(url, { observe: 'response' })
            .pipe(
                map(response => {
                    console.log("keys: " + response.headers.keys());
                    return response.body;
                }),
                tap(provider => this.log(`getProvider `)),
                catchError(this.handleError('Provider error', []))
            );
    }
    else {
        of(null);
    }
}

this return only 2 headers without the "etag" header:

keys: content-type,cache-control

but int the network tab :

my asp (mvc) Web api is configured to accpet CORS:

    <httpProtocol>
  <customHeaders>
    <add name="Access-Control-Allow-Origin" value="*" />
    <add name="Access-Control-Allow-Credentials" value="true" />
    <add name="Access-Control-Allow-Headers" value= "etag, Accept, Accept-CH, Accept-Charset, Accept-Datetime, Accept-Encoding, Accept-Ext, Accept-Features, Accept-Language, Accept-Params, Accept-Ranges, Access-Control-Allow-Credentials, Access-Control-Allow-Headers, Access-Control-Allow-Methods, Access-Control-Allow-Origin, Access-Control-Expose-Headers, Access-Control-Max-Age, Access-Control-Request-Headers, Access-Control-Request-Method, Age, Allow, Alternates, Authentication-Info, Authorization, C-Ext, C-Man, C-Opt, C-PEP, C-PEP-Info, CONNECT, Cache-Control, Compliance, Connection, Content-Base, Content-Disposition, Content-Encoding, Content-ID, Content-Language, Content-Length, Content-Location, Content-MD5, Content-Range, Content-Script-Type, Content-Security-Policy, Content-Style-Type, Content-Transfer-Encoding, Content-Type, Content-Version, Cookie, Cost, DAV, DELETE, DNT, DPR, Date, Default-Style, Delta-Base, Depth, Derived-From, Destination, Differential-ID, Digest, ETag, Expect, Expires, Ext, From, GET, GetProfile, HEAD, HTTP-date, Host, IM, If, If-Match, If-Modified-Since, If-None-Match, If-Range, If-Unmodified-Since, Keep-Alive, Label, Last-Event-ID, Last-Modified, Link, Location, Lock-Token, MIME-Version, Man, Max-Forwards, Media-Range, Message-ID, Meter, Negotiate, Non-Compliance, OPTION, OPTIONS, OWS, Opt, Optional, Ordering-Type, Origin, Overwrite, P3P, PEP, PICS-Label, POST, PUT, Pep-Info, Permanent, Position, Pragma, ProfileObject, Protocol, Protocol-Query, Protocol-Request, Proxy-Authenticate, Proxy-Authentication-Info, Proxy-Authorization, Proxy-Features, Proxy-Instruction, Public, RWS, Range, Referer, Refresh, Resolution-Hint, Resolver-Location, Retry-After, Safe, Sec-Websocket-Extensions, Sec-Websocket-Key, Sec-Websocket-Origin, Sec-Websocket-Protocol, Sec-Websocket-Version, Security-Scheme, Server, Set-Cookie, Set-Cookie2, SetProfile, SoapAction, Status, Status-URI, Strict-Transport-Security, SubOK, Subst, Surrogate-Capability, Surrogate-Control, TCN, TE, TRACE, Timeout, Title, Trailer, Transfer-Encoding, UA-Color, UA-Media, UA-Pixels, UA-Resolution, UA-Windowpixels, URI, Upgrade, User-Agent, Variant-Vary, Vary, Version, Via, Viewport-Width, WWW-Authenticate, Want-Digest, Warning, Width, X-Content-Duration, X-Content-Security-Policy, X-Content-Type-Options, X-CustomHeader, X-DNSPrefetch-Control, X-Forwarded-For, X-Forwarded-Port, X-Forwarded-Proto, X-Frame-Options, X-Modified, X-OTHER, X-PING, X-PINGOTHER, X-Powered-By, X-Requested-With"/>
    <add name="Access-Control-Allow-Methods" value="GET, POST, OPTIONS, PUT, DELETE" />
  </customHeaders>
</httpProtocol>

do have any idea how to get this header please ?

回答1:

solution is to add Access-Control-Expose-Headers:

 <add name="Access-Control-Expose-Headers" value="etag, Cache-Control, Content-Language, Content-Type, Expires, Last-Modified, Pragma" />

来源：https://stackoverflow.com/questions/51040216/httpclient-dont-return-all-headers

标签

httpclient

angular6