add details errors to host selection

go.mod

@@ -1,23 +1,28 @@
 module github.com/gocql/gocql
 
 require (
-	github.com/bitly/go-hostpool v0.0.0-20171023180738-a3a6125de932 // indirect
-	github.com/bmizerany/assert v0.0.0-20160611221934-b7ed37b82869 // indirect
-	github.com/golang/snappy v0.0.3
-	github.com/google/go-cmp v0.4.0
+	github.com/golang/snappy v0.0.4
+	github.com/google/go-cmp v0.5.9
 	github.com/hailocab/go-hostpool v0.0.0-20160125115350-e80d13ce29ed
-	github.com/kr/pretty v0.1.0 // indirect
-	github.com/stretchr/testify v1.3.0 // indirect
-	golang.org/x/net v0.0.0-20220526153639-5463443f8c37
+	golang.org/x/net v0.15.0
 	gopkg.in/inf.v0 v0.9.1
 	sigs.k8s.io/yaml v1.3.0
 )
 
+require (
+	github.com/bitly/go-hostpool v0.0.0-20171023180738-a3a6125de932 // indirect
+	github.com/bmizerany/assert v0.0.0-20160611221934-b7ed37b82869 // indirect
+	github.com/kr/pretty v0.3.1 // indirect
+	github.com/rogpeppe/go-internal v1.11.0 // indirect
+	gopkg.in/check.v1 v1.0.0-20201130134442-10cb98267c6c // indirect
+	gopkg.in/yaml.v2 v2.4.0 // indirect
+)
+
 retract (
-    v1.8.0  // tag from kiwicom/gocql added by mistake to scylladb/gocql
-    v1.8.1  // tag from kiwicom/gocql added by mistake to scylladb/gocql
-    v1.9.0  // tag from kiwicom/gocql added by mistake to scylladb/gocql
-    v1.10.0 // tag from kiwicom/gocql added by mistake to scylladb/gocql
+	v1.10.0 // tag from kiwicom/gocql added by mistake to scylladb/gocql
+	v1.9.0 // tag from kiwicom/gocql added by mistake to scylladb/gocql
+	v1.8.1 // tag from kiwicom/gocql added by mistake to scylladb/gocql
+	v1.8.0 // tag from kiwicom/gocql added by mistake to scylladb/gocql
 )
 
-go 1.13
+go 1.20

go.sum

@@ -2,36 +2,20 @@ github.com/bitly/go-hostpool v0.0.0-20171023180738-a3a6125de932 h1:mXoPYz/Ul5HYE
 github.com/bitly/go-hostpool v0.0.0-20171023180738-a3a6125de932/go.mod h1:NOuUCSz6Q9T7+igc/hlvDOUdtWKryOrtFyIVABv/p7k=
 github.com/bmizerany/assert v0.0.0-20160611221934-b7ed37b82869 h1:DDGfHa7BWjL4YnC6+E63dPcxHo2sUxDIu8g3QgEJdRY=
 github.com/bmizerany/assert v0.0.0-20160611221934-b7ed37b82869/go.mod h1:Ekp36dRnpXw/yCqJaO+ZrUyxD+3VXMFFr56k5XYrpB4=
-github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
 github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
-github.com/golang/snappy v0.0.3 h1:fHPg5GQYlCeLIPB9BZqMVR5nR9A+IM5zcgeTdjMYmLA=
-github.com/golang/snappy v0.0.3/go.mod h1:/XxbfmMg8lxefKM7IXC3fBNl/7bRcc72aCRzEWrmP2Q=
-github.com/google/go-cmp v0.4.0 h1:xsAVV57WRhGj6kEIi8ReJzQlHHqcBYCElAvkovg3B/4=
-github.com/google/go-cmp v0.4.0/go.mod h1:v8dTdLbMG2kIc/vJvl+f65V22dbkXbowE6jgT/gNBxE=
+github.com/golang/snappy v0.0.4 h1:yAGX7huGHXlcLOEtBnF4w7FQwA26wojNCwOYAEhLjQM=
+github.com/google/go-cmp v0.5.9 h1:O2Tfq5qg4qc4AmwVlvv0oLiVAGB7enBSJ2x2DqQFi38=
 github.com/hailocab/go-hostpool v0.0.0-20160125115350-e80d13ce29ed h1:5upAirOpQc1Q53c0bnx2ufif5kANL7bfZWcc6VJWJd8=
 github.com/hailocab/go-hostpool v0.0.0-20160125115350-e80d13ce29ed/go.mod h1:tMWxXQ9wFIaZeTI9F+hmhFiGpFmhOHzyShyFUhRm0H4=
-github.com/kr/pretty v0.1.0 h1:L/CwN0zerZDmRFUapSPitk6f+Q3+0za1rQkzVuMiMFI=
-github.com/kr/pretty v0.1.0/go.mod h1:dAy3ld7l9f0ibDNOQOHHMYYIIbhfbHSm3C4ZsoJORNo=
+github.com/kr/pretty v0.3.1 h1:flRD4NNwYAUpkphVc1HcthR4KEIFJ65n8Mw5qdRn3LE=
 github.com/kr/pty v1.1.1/go.mod h1:pFQYn66WHrOpPYNljwOMqo10TkYh1fy3cYio2l3bCsQ=
-github.com/kr/text v0.1.0 h1:45sCR5RtlFHMR4UwH9sdQ5TC8v0qDQCHnXt+kaKSTVE=
 github.com/kr/text v0.1.0/go.mod h1:4Jbv+DJW3UT/LiOwJeYQe1efqtUx/iVham/4vfdArNI=
-github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
-github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
-github.com/stretchr/objx v0.1.0/go.mod h1:HFkY916IF+rwdDfMAkV7OtwuqBVzrE8GR6GFx+wExME=
-github.com/stretchr/testify v1.3.0 h1:TivCn/peBQ7UY8ooIcPgZFpTNSz0Q2U6UrFlUfqbe0Q=
-github.com/stretchr/testify v1.3.0/go.mod h1:M5WIy9Dh21IEIfnGCwXGc5bZfKNJtfHm1UVUgZn+9EI=
-golang.org/x/net v0.0.0-20220526153639-5463443f8c37 h1:lUkvobShwKsOesNfWWlCS5q7fnbG1MEliIzwu886fn8=
-golang.org/x/net v0.0.0-20220526153639-5463443f8c37/go.mod h1:XRhObCWvk6IyKnWLug+ECip1KBveYUHfp+8e9klMJ9c=
-golang.org/x/sys v0.0.0-20210615035016-665e8c7367d1/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
-golang.org/x/sys v0.0.0-20220520151302-bc2c85ada10a/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
-golang.org/x/term v0.0.0-20210927222741-03fcf44c2211/go.mod h1:jbD1KX2456YbFQfuXm/mYQcufACuNUgVhRMnK/tPxf8=
-golang.org/x/text v0.3.7/go.mod h1:u+2+/6zg+i71rQMx5EYifcz6MCKuco9NR6JIITiCfzQ=
-golang.org/x/tools v0.0.0-20180917221912-90fa682c2a6e/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
-golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543 h1:E7g+9GITq07hpfrRu66IVDexMakfv52eLZ2CXBWiKr4=
-golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
-gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
+github.com/kr/text v0.2.0 h1:5Nx0Ya0ZqY2ygV366QzturHI13Jq95ApcVaJBhpS+AY=
+github.com/rogpeppe/go-internal v1.11.0 h1:cWPaGQEPrBb5/AsnsZesgZZ9yb1OQ+GOISoDNXVBh4M=
+golang.org/x/net v0.15.0 h1:ugBLEUaxABaB5AJqW9enI0ACdci2RUd4eP51NTBvuJ8=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
+gopkg.in/check.v1 v1.0.0-20201130134442-10cb98267c6c h1:Hei/4ADfdWqJk1ZMxUNpqntNwaWcugrBjAiHlqqRiVk=
 gopkg.in/inf.v0 v0.9.1 h1:73M5CoZyi3ZLMOyDlQh031Cx6N9NDJ2Vvfl76EDAgDc=
 gopkg.in/inf.v0 v0.9.1/go.mod h1:cWUDdTG/fYaXco+Dcufb5Vnc6Gp2YChqWtbxRZE0mXw=
 gopkg.in/yaml.v2 v2.4.0 h1:D8xgwECY7CYvx+Y2n4sBz93Jn9JRvxdiyyo8CTfuKaY=

query_executor.go

@@ -2,6 +2,8 @@ package gocql
 
 import (
 	"context"
+	"errors"
+	"fmt"
 	"sync"
 	"time"
 )
@@ -108,23 +110,27 @@ func (q *queryExecutor) do(ctx context.Context, qry ExecutableQuery, hostIter Ne
 	selectedHost := hostIter()
 	rt := qry.retryPolicy()
 
-	var lastErr error
+	var errs []error
+
 	var iter *Iter
 	for selectedHost != nil {
 		host := selectedHost.Info()
 		if host == nil || !host.IsUp() {
+			errs = append(errs, ErrSelectHost{host: host, cause: ErrHostNilOrDown})
 			selectedHost = hostIter()
 			continue
 		}
 
 		pool, ok := q.pool.getPool(host)
 		if !ok {
+			errs = append(errs, ErrSelectHost{host: host, cause: ErrNoConnPool})
 			selectedHost = hostIter()
 			continue
 		}
 
 		conn := pool.Pick(selectedHost.Token())
 		if conn == nil {
+			errs = append(errs, ErrSelectHost{host: host, cause: ErrNoConnInHostPool})
 			selectedHost = hostIter()
 			continue
 		}
@@ -147,7 +153,7 @@ func (q *queryExecutor) do(ctx context.Context, qry ExecutableQuery, hostIter Ne
 		if iter.err == nil || rt == nil || !rt.Attempt(qry) {
 			return iter
 		}
-		lastErr = iter.err
+		errs = append(errs, ErrSelectHost{host: host, cause: iter.err})
 
 		// If query is unsuccessful, check the error with RetryPolicy to retry
 		switch rt.GetRetryType(iter.err) {
@@ -166,13 +172,30 @@ func (q *queryExecutor) do(ctx context.Context, qry ExecutableQuery, hostIter Ne
 		}
 	}
 
-	if lastErr != nil {
-		return &Iter{err: lastErr}
+	if len(errs) > 0 {
+		return &Iter{err: errors.Join(errs...)}
 	}
 
 	return &Iter{err: ErrNoConnections}
 }
 
+var ErrHostNilOrDown = errors.New("gocql: host nil or down")
+var ErrNoConnPool = errors.New("gocql: no connection pool for host")
+var ErrNoConnInHostPool = errors.New("gocql: no connection to pick in host pool")
+
+type ErrSelectHost struct {
+	host  *HostInfo
+	cause error
+}
+
+func (err ErrSelectHost) Error() string {
+	h := "unknown host"
+	if err.host != nil {
+		h = err.host.Hostname()
+	}
+	return fmt.Sprintf("%s: %v", h, err.cause)
+}
+
 func (q *queryExecutor) run(ctx context.Context, qry ExecutableQuery, hostIter NextHost, results chan<- *Iter) {
 	select {
 	case results <- q.do(ctx, qry, hostIter):