From io Reader to string in Go

Question

I have an io ReadCloser object  from an http Response object    What s the most efficient way to convert the entire stream to a string object

User · Answer

data       ioutil ReadAll response Body  fmt Println string data

User · Answer

The most efficient way would be to always use   byte instead of string   In case you need to print data received from the io ReadCloser  the fmt package can handle   byte  but it isn t efficient because the fmt implementation will internally convert   byte to string  In order to avoid this conversion  you can implement the fmt Formatter interface for a type like type ByteSlice   byte

User · Answer

func copyToString r io Reader   res string  err error        var sb strings Builder     if    err   io Copy  amp sb  r   err    nil           res   sb String             return

User · Answer

var b bytes Buffer b ReadFrom r      b String

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I like the bytes Buffer struct   I see it has ReadFrom and String methods   I ve used it with a   byte but not an io Reader

User · Answer

Answers so far haven t addressed the  quot entire stream quot  part of the question   I think the good way to do this is ioutil ReadAll   With your io ReaderCloser named rc  I would write  Go  gt   v1 16 if b  err    io ReadAll rc   err    nil       return string b         Go  lt   v1 15 if b  err    ioutil ReadAll rc   err    nil       return string b

User · Answer

EDIT   Since 1 10  strings Builder exists  Example   buf    new strings Builder  n  err    io Copy buf  r     check errors fmt Println buf String        OUTDATED INFORMATION BELOW  The short answer is that it it will not be efficient because converting to a string requires doing a complete copy of the byte array  Here is the proper  non-efficient  way to do what you want   buf    new bytes Buffer  buf ReadFrom yourReader  s    buf String      Does a complete copy of the bytes in the buffer    This copy is done as a protection mechanism  Strings are immutable  If you could convert a   byte to a string  you could change the contents of the string  However  go allows you to disable the type safety mechanisms using the unsafe package  Use the unsafe package at your own risk  Hopefully the name alone is a good enough warning  Here is how I would do it using unsafe   buf    new bytes Buffer  buf ReadFrom yourReader  b    buf Bytes   s       string  unsafe Pointer  amp b     There we go  you have now efficiently converted your byte array to a string  Really  all this does is trick the type system into calling it a string  There are a couple caveats to this method    There are no guarantees this will work in all go compilers  While this works with the plan-9 gc compiler  it relies on  implementation details  not mentioned in the official spec  You can not even guarantee that this will work on all architectures or not be changed in gc  In other words  this is a bad idea  That string is mutable  If you make any calls on that buffer it will change the string  Be very careful    My advice is to stick to the official method  Doing a copy is not that expensive and it is not worth the evils of unsafe  If the string is too large to do a copy  you should not be making it into a string

[go] From io.Reader to string in Go

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