feat: add GetQueryParam method to support pagination

v5/core/utils.go

@@ -18,6 +18,7 @@ import (
  "encoding/json"
  "errors"
  "fmt"
+ "net/url"
  "os"
  "reflect"
  "regexp"
@@ -261,3 +262,27 @@ func SliceContains(slice []string, contains string) bool {
  }
  return false
 }
+
+// return a pointer to the value of query parameter `param` from url,
+// or nil when not found
+func GetQueryParam(urlStr *string, param string) (*string, error) {
+ if urlStr == nil || *urlStr == "" {
+ return nil, nil
+ }
+
+ u, err := url.Parse(*urlStr)
+ if err != nil {
+ return nil, err
+ }
+
+ q, err := url.ParseQuery(u.RawQuery)
+ if err != nil {
+ return nil, err
+ }
+
+ v := q.Get(param)
+ if v == "" {
+ return nil, nil
+ }
+ return &v, nil
+}

v5/core/utils_test.go

@@ -480,3 +480,55 @@ func TestSliceContains(t *testing.T) {
 
  assert.False(t, SliceContains(nil, "foo"))
 }
+
+func TestGetQueryParam(t *testing.T) {
+ nextURL := "/api/v1/offerings?start=foo&limit=10"
+ next, err := GetQueryParam(&nextURL, "start")
+ assert.Nil(t, err)
+ assert.Equal(t, "foo", *next)
+
+ fqNextURL := "https://acme.com/api/v1/offerings?start=bar&limit=10"
+ next, err = GetQueryParam(&fqNextURL, "start")
+ assert.Nil(t, err)
+ assert.Equal(t, "bar", *next)
+
+ // No query parameter
+ next, err = GetQueryParam(&nextURL, "token")
+ assert.Nil(t, err)
+ assert.Nil(t, next)
+
+ // nil URL
+ next, err = GetQueryParam(nil, "start")
+ assert.Nil(t, err)
+ assert.Nil(t, next)
+
+ // empty URL
+ var emptyURL string
+ next, err = GetQueryParam(&emptyURL, "start")
+ assert.Nil(t, err)
+ assert.Nil(t, next)
+
+ // Not a URL (parse fails)
+ badURL := "https://foo.bar:baz/api/v1/offerings?start=foo"
+ next, err = GetQueryParam(&badURL, "start")
+ assert.NotNil(t, err)
+ assert.Nil(t, next)
+
+ // No query string
+ noQueryStringURL := "/api/v1/offerings"
+ next, err = GetQueryParam(&noQueryStringURL, "start")
+ assert.Nil(t, err)
+ assert.Nil(t, next)
+
+ // Bad query string
+ badQueryURL := "/api/v1/offerings?start%XXfoo"
+ next, err = GetQueryParam(&badQueryURL, "start")
+ assert.NotNil(t, err)
+ assert.Nil(t, next)
+
+ // Duplicate param
+ dupParamURL := "/api/v1/offerings?start=foo&start=bar&limit=10"
+ next, err = GetQueryParam(&dupParamURL, "start")
+ assert.Nil(t, err)
+ assert.Equal(t, "foo", *next)
+}