{"id":5198,"date":"2021-03-03T21:11:03","date_gmt":"2021-03-03T15:41:03","guid":{"rendered":"https:\/\/golangbyexamples.com\/?p=5198"},"modified":"2021-03-03T21:11:12","modified_gmt":"2021-03-03T15:41:12","slug":"http-no-redirect-client-golang","status":"publish","type":"post","link":"https:\/\/golangbyexamples.com\/http-no-redirect-client-golang\/","title":{"rendered":"HTTP Client to not follow redirect in Go (Golang)"},"content":{"rendered":"\n<div id=\"ez-toc-container\" class=\"ez-toc-v2_0_17 counter-hierarchy counter-decimal ez-toc-light-blue\">\n<div class=\"ez-toc-title-container\">\n<p class=\"ez-toc-title\">Table of Contents<\/p>\n<span class=\"ez-toc-title-toggle\"><a class=\"ez-toc-pull-right ez-toc-btn ez-toc-btn-xs ez-toc-btn-default ez-toc-toggle\" style=\"display: none;\"><i class=\"ez-toc-glyphicon ez-toc-icon-toggle\"><\/i><\/a><\/span><\/div>\n<nav><ul class=\"ez-toc-list ez-toc-list-level-1\"><li class=\"ez-toc-page-1 ez-toc-heading-level-1\"><a class=\"ez-toc-link ez-toc-heading-1\" href=\"https:\/\/golangbyexamples.com\/http-no-redirect-client-golang\/#Overview\" title=\"Overview\">Overview<\/a><\/li><li class=\"ez-toc-page-1 ez-toc-heading-level-1\"><a class=\"ez-toc-link ez-toc-heading-2\" href=\"https:\/\/golangbyexamples.com\/http-no-redirect-client-golang\/#CheckDirect_is_nil\" title=\"CheckDirect is nil\">CheckDirect is nil<\/a><\/li><li class=\"ez-toc-page-1 ez-toc-heading-level-1\"><a class=\"ez-toc-link ez-toc-heading-3\" href=\"https:\/\/golangbyexamples.com\/http-no-redirect-client-golang\/#CheckDirect_is_not-nil\" title=\"CheckDirect is not-nil\">CheckDirect is not-nil<\/a><\/li><\/ul><\/nav><\/div>\n<h1 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"Overview\"><\/span><strong>Overview<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h1>\n\n\n\n<p class=\"has-medium-font-size\"><strong>http.Client<\/strong> struct is used to make HTTP requests in golang. <\/p>\n\n\n\n<p class=\"has-medium-font-size\"><a href=\"https:\/\/golang.org\/src\/net\/http\/client.go\">https:\/\/golang.org\/src\/net\/http\/client.go<\/a><\/p>\n\n\n\n<p class=\"has-medium-font-size\"><strong>http.Client<\/strong> lets you specify a policy of how redirects can be handled.&nbsp; Below is the structure of <strong>http.Client <\/strong>struct<\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">type Client struct {\n\tTransport RoundTripper\n\tCheckRedirect func(req *Request, via []*Request) error\n\tJar CookieJar\n\tTimeout time.Duration\n}<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\">The <strong>CheckRedirect<\/strong> field is a function actually which lets you specify a way of how redirects can be handled. This function is called before following any future redirects. So basically whenever the server responds with a redirect the client will first call the <strong>CheckRedirect<\/strong> function to check if redirect should be followed or not. Below is the signature of the <strong>CheckRedirect<\/strong> function<\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">func(req *Request, via []*Request) error<\/code><\/pre>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>The first parameter <strong>req<\/strong> is the upcoming request<\/li><\/ul>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>The second parameter <strong>via<\/strong> is the requests already made. That is why it is a slice. The first element is the oldest request.<\/li><\/ul>\n\n\n\n<p class=\"has-medium-font-size\">There are two cases to consider<\/p>\n\n\n\n<h1 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"CheckDirect_is_nil\"><\/span><strong>CheckDirect is nil<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h1>\n\n\n\n<p class=\"has-medium-font-size\">You don&#8217;t specify the CheckRedirect field during the initialization of <strong>http.Client<\/strong> struct. In this case, default behavior kicks in, and the HTTP client will follow 10 redirects, and then it will return an error.&nbsp; Below is the <strong>defaultCheckRedirect<\/strong> function which quits after 10 retries.<\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">func defaultCheckRedirect(req *Request, via []*Request) error {\n\tif len(via) >= 10 {\n\t\treturn errors.New(\"stopped after 10 redirects\")\n\t}\n\treturn nil\n}<\/code><\/pre>\n\n\n\n<h1 class=\"wp-block-heading\"><span class=\"ez-toc-section\" id=\"CheckDirect_is_not-nil\"><\/span><strong>CheckDirect is not-nil<\/strong><span class=\"ez-toc-section-end\"><\/span><\/h1>\n\n\n\n<p class=\"has-medium-font-size\">You specify your own <strong>CheckRedirect<\/strong> function during the initialization of the <strong>http.Client<\/strong> struct. When you specify this function, then this function will be called before following any future redirect.&nbsp; When you write your own CheckRedirect function you need to know the below things in mind<br>When the <strong>CheckRedirect<\/strong> function returns an error, then the HTTP client will return two things<\/p>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>The previous response along with body closed<\/li><\/ul>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>The actual error (wrapped in a <strong>url.Error)<\/strong><\/li><\/ul>\n\n\n\n<p class=\"has-medium-font-size\"><strong><\/strong>There is also a special case when <strong>CheckRedirect<\/strong> function returns <strong>ErrUseLastResponse <\/strong>error. In this case, the client will return<\/p>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>Most recent response along with body unclosed<\/li><\/ul>\n\n\n\n<ul class=\"has-medium-font-size wp-block-list\"><li>Non-nil error<\/li><\/ul>\n\n\n\n<p class=\"has-medium-font-size\">So basically when you don&#8217;t want HTTP Client to follow the redirect, then please specify your own <strong>CheckRedirect<\/strong> function to control the behavior the way you want.&nbsp; For example below is one sample <strong>CheckRedirect <\/strong>function that will inform HTTP client to not follow any redirect and also not return any error, just return the last response along with body unclosed.<\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">func MyCheckRedirect(req *Request, via []*Request) error {\n\treturn http.ErrUseLastResponse\n}<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\">Here is the definition of <strong>ErrUseLastResponse <\/strong>in the http package<\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">var ErrUseLastResponse = errors.New(\"net\/http: use last response\")<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\">Create <strong>http.Client<\/strong> as below specifying the <strong>CheckRedirect<\/strong> function<\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">client := &http.Client{\n    CheckRedirect: func(req *Request, via []*Request) error {\n\treturn http.ErrUseLastResponse\n    },\n}<\/code><\/pre>\n\n\n\n<p class=\"has-medium-font-size\">Here is another sample <strong>CheckRedirect <\/strong>function which will only follow redirect two times and then return the error<\/p>\n\n\n\n<pre class=\"wp-block-prismatic-blocks\"><code class=\"language-go\">func MyCheckRedirect(req *Request, via []*Request) error {\n\tif len(via) >= 2 {\n\t\treturn errors.New(\"stopped after 10 redirects\")\n\t}\n\treturn nil\n}<\/code><\/pre>\n","protected":false},"excerpt":{"rendered":"<p>Table of Contents OverviewCheckDirect is nilCheckDirect is not-nil Overview http.Client struct is used to make HTTP requests in golang. https:\/\/golang.org\/src\/net\/http\/client.go http.Client lets you specify a policy of how redirects can be handled.&nbsp;&#8230;<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"spay_email":"","footnotes":"","jetpack_publicize_message":"","jetpack_is_tweetstorm":false},"categories":[1],"tags":[314],"class_list":["post-5198","post","type-post","status-publish","format-standard","hentry","category-tech","tag-redirect"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v22.7 - 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