Golang read request body

Question

I am writing my own logginMiddleware  Basically  I need to log body of the request and the response  The problem that I faced is that when I read body  it becomes empty and I cannot read it twice   I understand that it happens because it is of type ReadCloser  Is there a way to rewind body to the beginning

User · Answer

I could use the GetBody from Request package   Look this comment in source code from request go in net http      GetBody defines an optional func to return a new copy of   Body  It is used for client requests when a redirect requires   reading the body more than once  Use of GetBody still   requires setting Body    For server requests it is unused     GetBody func    io ReadCloser  error   This way you can get the body request without make it empty   Sample   getBody    request GetBody copyBody  err    getBody   if err    nil          Do something return err   http DefaultClient Do request

User · Answer

Inspecting and mocking request body  When you first read the body  you have to store it so once you re done with it  you can set a new io ReadCloser as the request body constructed from the original data  So when you advance in the chain  the next handler can read the same body   One option is to read the whole body using ioutil ReadAll    which gives you the body as a byte slice   You may use bytes NewBuffer   to obtain an io Reader from a byte slice   The last missing piece is to make the io Reader an io ReadCloser  because bytes Buffer does not have a Close   method  For this you may use ioutil NopCloser   which wraps an io Reader  and returns an io ReadCloser  whose added Close   method will be a no-op  does nothing    Note that you may even modify the contents of the byte slice you use to create the  new  body  You have full control over it   Care must be taken though  as there might be other HTTP fields like content-length and checksums which may become invalid if you modify only the data  If subsequent handlers check those  you would also need to modify those too   Inspecting   modifying response body  If you also want to read the response body  then you have to wrap the http ResponseWriter you get  and pass the wrapper on the chain  This wrapper may cache the data sent out  which you can inspect either after  on on-the-fly  as the subsequent handlers write to it    Here s a simple ResponseWriter wrapper  which just caches the data  so it ll be available after the subsequent handler returns   type MyResponseWriter struct       http ResponseWriter     buf  bytes Buffer    func  mrw  MyResponseWriter  Write p   byte   int  error        return mrw buf Write p      Note that MyResponseWriter Write   just writes the data to a buffer  You may also choose to inspect it on-the-fly  in the Write   method  and write the data immediately to the wrapped   embedded ResponseWriter  You may even modify the data  You have full control   Care must be taken again though  as the subsequent handlers may also send HTTP response headers related to the response data    such as length or checksums    which may also become invalid if you alter the response data   Full example  Putting the pieces together  here s a full working example   func loginmw handler http Handler  http Handler       return http HandlerFunc func w http ResponseWriter  r  http Request            body  err    ioutil ReadAll r Body          if err    nil               log Printf  Error reading body   v   err              http Error w   can t read body   http StatusBadRequest              return                       Work   inspect body  You may even modify it              And now set a new body  which will simulate the same data we read          r Body   ioutil NopCloser bytes NewBuffer body               Create a response wrapper          mrw     amp MyResponseWriter              ResponseWriter  w              buf              amp bytes Buffer                          Call next handler  passing the response wrapper          handler ServeHTTP mrw  r              Now inspect response  and finally send it out              You can also modify it before sending it out           if    err    io Copy w  mrw buf   err    nil               log Printf  Failed to send out response   v   err

[http] Golang read request body

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