Detect "copy" if the SQL string starts with whitespace or comments

Previously it was just strings.EqualFold(q[:4], "COPY"), and would fail
to detect e.g. "/* foo */ copy [..]" or "  copy".

There is a small ~15ns performance hit for this, which seems acceptable.

Co-authored-by: Dario Castañé <[email protected]>

Author: arp242

conn.go

@@ -24,6 +24,7 @@ import (
 	"sync"
 	"time"
 
+	"github.com/lib/pq/internal/pqsql"
 	"github.com/lib/pq/internal/proto"
 	"github.com/lib/pq/oid"
 	"github.com/lib/pq/scram"
@@ -795,7 +796,7 @@ func (cn *conn) Prepare(q string) (_ driver.Stmt, err error) {
 	}
 	defer cn.errRecover(&err, q)
 
-	if len(q) >= 4 && strings.EqualFold(q[:4], "COPY") {
+	if pqsql.StartsWithCopy(q) {
 		s, err := cn.prepareCopyIn(q)
 		if err == nil {
 			cn.inCopy = true

conn_test.go

@@ -125,7 +125,7 @@ server:5432:some_db:some_user:pass_A
 *:5432:some_db:some_user:pass_B
 localhost:*:*:*:pass_C
 *:*:*:*:pass_fallback
-`)
+	`)
 	if err != nil {
 		t.Fatalf("Unexpected error writing pgpass file %#v", err)
 	}
@@ -290,8 +290,6 @@ func TestStatment(t *testing.T) {
 		t.Fatalf("expected 1, got %d", i)
 	}
 
-	// st1
-
 	r1, err := st1.Query()
 	if err != nil {
 		t.Fatal(err)
@@ -876,13 +874,14 @@ func TestQueryRowBugWorkaround(t *testing.T) {
 		t.Fatalf("could not disable check_function_bodies: %s", err)
 	}
 	_, err = tx.Exec(`
-CREATE OR REPLACE FUNCTION bad_function()
-RETURNS integer
--- hack to prevent the function from being inlined
-SET check_function_bodies TO TRUE
-AS $$
-	SELECT text 'bad'
-$$ LANGUAGE sql`)
+		CREATE OR REPLACE FUNCTION bad_function()
+		RETURNS integer
+		-- hack to prevent the function from being inlined
+		SET check_function_bodies TO TRUE
+		AS $$
+			SELECT text 'bad'
+		$$ LANGUAGE sql
+	`)
 	if err != nil {
 		t.Fatalf("could not create function: %s", err)
 	}
@@ -907,11 +906,11 @@ $$ LANGUAGE sql`)
 	// Also test that simpleQuery()'s workaround works when the query fails
 	// after a row has been received.
 	rows, err := db.Query(`
-select
-	(select generate_series(1, ss.i))
-from (select gs.i
-      from generate_series(1, 2) gs(i)
-      order by gs.i limit 2) ss`)
+		select (select generate_series(1, ss.i))
+		from (select gs.i
+			from generate_series(1, 2) gs(i)
+			order by gs.i limit 2) ss
+	`)
 	if err != nil {
 		t.Fatalf("query failed: %s", err)
 	}

copy_test.go

@@ -316,7 +316,7 @@ func TestCopyFromError(t *testing.T) {
 	if err != nil {
 		t.Fatal(err)
 	}
-	_, err = txn.Prepare("COPY temp (num) TO STDOUT")
+	_, err = txn.Prepare("-- comment\n  /* comment */  COPY temp (num) TO STDOUT")
 	if err != errCopyToNotSupported {
 		t.Fatalf("expected %s, got %+v", errCopyToNotSupported, err)
 	}
@@ -474,10 +474,47 @@ func BenchmarkCopyIn(b *testing.B) {
 	}
 }
 
-var bigTableColumns = []string{"ABIOGENETICALLY", "ABORIGINALITIES", "ABSORBABILITIES", "ABSORBEFACIENTS", "ABSORPTIOMETERS", "ABSTRACTIONISMS", "ABSTRACTIONISTS", "ACANTHOCEPHALAN", "ACCEPTABILITIES", "ACCEPTINGNESSES", "ACCESSARINESSES", "ACCESSIBILITIES", "ACCESSORINESSES", "ACCIDENTALITIES", "ACCIDENTOLOGIES", "ACCLIMATISATION", "ACCLIMATIZATION", "ACCOMMODATINGLY", "ACCOMMODATIONAL", "ACCOMPLISHMENTS", "ACCOUNTABLENESS", "ACCOUNTANTSHIPS", "ACCULTURATIONAL", "ACETOPHENETIDIN", "ACETYLSALICYLIC", "ACHONDROPLASIAS", "ACHONDROPLASTIC", "ACHROMATICITIES", "ACHROMATISATION", "ACHROMATIZATION", "ACIDIMETRICALLY", "ACKNOWLEDGEABLE", "ACKNOWLEDGEABLY", "ACKNOWLEDGEMENT", "ACKNOWLEDGMENTS", "ACQUIRABILITIES", "ACQUISITIVENESS", "ACRIMONIOUSNESS", "ACROPARESTHESIA", "ACTINOBIOLOGIES", "ACTINOCHEMISTRY", "ACTINOTHERAPIES", "ADAPTABLENESSES", "ADDITIONALITIES", "ADENOCARCINOMAS", "ADENOHYPOPHYSES", "ADENOHYPOPHYSIS", "ADENOIDECTOMIES", "ADIATHERMANCIES", "ADJUSTABILITIES", "ADMINISTRATIONS", "ADMIRABLENESSES", "ADMISSIBILITIES", "ADRENALECTOMIES", "ADSORBABILITIES", "ADVENTUROUSNESS", "ADVERSARINESSES", "ADVISABLENESSES", "AERODYNAMICALLY", "AERODYNAMICISTS", "AEROELASTICIANS", "AEROHYDROPLANES", "AEROLITHOLOGIES", "AEROSOLISATIONS", "AEROSOLIZATIONS", "AFFECTABILITIES", "AFFECTIVENESSES", "AFFORDABILITIES", "AFFRANCHISEMENT", "AFTERSENSATIONS", "AGGLUTINABILITY", "AGGRANDISEMENTS", "AGGRANDIZEMENTS", "AGGREGATENESSES", "AGRANULOCYTOSES", "AGRANULOCYTOSIS", "AGREEABLENESSES", "AGRIBUSINESSMAN", "AGRIBUSINESSMEN", "AGRICULTURALIST", "AIRWORTHINESSES", "ALCOHOLISATIONS", "ALCOHOLIZATIONS", "ALCOHOLOMETRIES", "ALEXIPHARMAKONS", "ALGORITHMICALLY", "ALKALINISATIONS", "ALKALINIZATIONS", "ALLEGORICALNESS", "ALLEGORISATIONS", "ALLEGORIZATIONS", "ALLELOMORPHISMS", "ALLERGENICITIES", "ALLOTETRAPLOIDS", "ALLOTETRAPLOIDY", "ALLOTRIOMORPHIC", "ALLOWABLENESSES", "ALPHABETISATION", "ALPHABETIZATION", "ALTERNATIVENESS", "ALTITUDINARIANS", "ALUMINOSILICATE", "ALUMINOTHERMIES", "AMARYLLIDACEOUS", "AMBASSADORSHIPS", "AMBIDEXTERITIES", "AMBIGUOUSNESSES", "AMBISEXUALITIES", "AMBITIOUSNESSES", "AMINOPEPTIDASES", "AMINOPHENAZONES", "AMMONIFICATIONS", "AMORPHOUSNESSES", "AMPHIDIPLOIDIES", "AMPHITHEATRICAL", "ANACOLUTHICALLY", "ANACREONTICALLY", "ANAESTHESIOLOGY", "ANAESTHETICALLY", "ANAGRAMMATISING", "ANAGRAMMATIZING", "ANALOGOUSNESSES", "ANALYZABILITIES", "ANAMORPHOSCOPES", "ANCYLOSTOMIASES", "ANCYLOSTOMIASIS", "ANDROGYNOPHORES", "ANDROMEDOTOXINS", "ANDROMONOECIOUS", "ANDROMONOECISMS", "ANESTHETIZATION", "ANFRACTUOSITIES", "ANGUSTIROSTRATE", "ANIMATRONICALLY", "ANISOTROPICALLY", "ANKYLOSTOMIASES", "ANKYLOSTOMIASIS", "ANNIHILATIONISM", "ANOMALISTICALLY", "ANOMALOUSNESSES", "ANONYMOUSNESSES", "ANSWERABILITIES", "ANTAGONISATIONS", "ANTAGONIZATIONS", "ANTAPHRODISIACS", "ANTEPENULTIMATE", "ANTHROPOBIOLOGY", "ANTHROPOCENTRIC", "ANTHROPOGENESES", "ANTHROPOGENESIS", "ANTHROPOGENETIC", "ANTHROPOLATRIES", "ANTHROPOLOGICAL", "ANTHROPOLOGISTS", "ANTHROPOMETRIES", "ANTHROPOMETRIST", "ANTHROPOMORPHIC", "ANTHROPOPATHIES", "ANTHROPOPATHISM", "ANTHROPOPHAGIES", "ANTHROPOPHAGITE", "ANTHROPOPHAGOUS", "ANTHROPOPHOBIAS", "ANTHROPOPHOBICS", "ANTHROPOPHUISMS", "ANTHROPOPSYCHIC", "ANTHROPOSOPHIES", "ANTHROPOSOPHIST", "ANTIABORTIONIST", "ANTIALCOHOLISMS", "ANTIAPHRODISIAC", "ANTIARRHYTHMICS", "ANTICAPITALISMS", "ANTICAPITALISTS", "ANTICARCINOGENS", "ANTICHOLESTEROL", "ANTICHOLINERGIC", "ANTICHRISTIANLY", "ANTICLERICALISM", "ANTICLIMACTICAL", "ANTICOINCIDENCE", "ANTICOLONIALISM", "ANTICOLONIALIST", "ANTICOMPETITIVE", "ANTICONVULSANTS", "ANTICONVULSIVES", "ANTIDEPRESSANTS", "ANTIDERIVATIVES", "ANTIDEVELOPMENT", "ANTIEDUCATIONAL", "ANTIEGALITARIAN", "ANTIFASHIONABLE", "ANTIFEDERALISTS", "ANTIFERROMAGNET", "ANTIFORECLOSURE", "ANTIHELMINTHICS", "ANTIHISTAMINICS", "ANTILIBERALISMS", "ANTILIBERTARIAN", "ANTILOGARITHMIC", "ANTIMATERIALISM", "ANTIMATERIALIST", "ANTIMETABOLITES", "ANTIMILITARISMS", "ANTIMILITARISTS", "ANTIMONARCHICAL", "ANTIMONARCHISTS", "ANTIMONOPOLISTS", "ANTINATIONALIST", "ANTINUCLEARISTS", "ANTIODONTALGICS", "ANTIPERISTALSES", "ANTIPERISTALSIS", "ANTIPERISTALTIC", "ANTIPERSPIRANTS", "ANTIPHLOGISTICS", "ANTIPORNOGRAPHY", "ANTIPROGRESSIVE", "ANTIQUARIANISMS", "ANTIRADICALISMS", "ANTIRATIONALISM", "ANTIRATIONALIST", "ANTIRATIONALITY", "ANTIREPUBLICANS", "ANTIROMANTICISM", "ANTISEGREGATION", "ANTISENTIMENTAL", "ANTISEPARATISTS", "ANTISEPTICISING", "ANTISEPTICIZING", "ANTISEXUALITIES", "ANTISHOPLIFTING", "ANTISOCIALITIES", "ANTISPECULATION", "ANTISPECULATIVE", "ANTISYPHILITICS", "ANTITHEORETICAL", "ANTITHROMBOTICS", "ANTITRADITIONAL", "ANTITRANSPIRANT", "ANTITRINITARIAN", "ANTITUBERCULOUS", "ANTIVIVISECTION", "APHELIOTROPISMS", "APOCALYPTICALLY", "APOCALYPTICISMS", "APOLIPOPROTEINS", "APOLITICALITIES", "APOPHTHEGMATISE", "APOPHTHEGMATIST", "APOPHTHEGMATIZE", "APOTHEGMATISING", "APOTHEGMATIZING", "APPEALABILITIES", "APPEALINGNESSES", "APPENDICULARIAN", "APPLICABILITIES", "APPRENTICEHOODS", "APPRENTICEMENTS", "APPRENTICESHIPS", "APPROACHABILITY", "APPROPINQUATING", "APPROPINQUATION", "APPROPINQUITIES", "APPROPRIATENESS", "ARACHNOIDITISES", "ARBITRARINESSES", "ARBORICULTURIST", "ARCHAEBACTERIUM", "ARCHAEOBOTANIES", "ARCHAEOBOTANIST", "ARCHAEOMETRISTS", "ARCHAEOPTERYXES", "ARCHAEZOOLOGIES", "ARCHEOASTRONOMY", "ARCHEOBOTANISTS", "ARCHEOLOGICALLY", "ARCHEOMAGNETISM", "ARCHEOZOOLOGIES", "ARCHEOZOOLOGIST", "ARCHGENETHLIACS", "ARCHIDIACONATES", "ARCHIEPISCOPACY", "ARCHIEPISCOPATE", "ARCHITECTURALLY", "ARCHPRIESTHOODS", "ARCHPRIESTSHIPS", "ARGUMENTATIVELY", "ARIBOFLAVINOSES", "ARIBOFLAVINOSIS", "AROMATHERAPISTS", "ARRONDISSEMENTS", "ARTERIALISATION", "ARTERIALIZATION", "ARTERIOGRAPHIES", "ARTIFICIALISING", "ARTIFICIALITIES", "ARTIFICIALIZING", "ASCLEPIADACEOUS", "ASSENTIVENESSES"}
-
 func BenchmarkCopy(b *testing.B) {
+	bigTableColumns := []string{"ABIOGENETICALLY", "ABORIGINALITIES", "ABSORBABILITIES", "ABSORBEFACIENTS", "ABSORPTIOMETERS", "ABSTRACTIONISMS",
+		"ABSTRACTIONISTS", "ACANTHOCEPHALAN", "ACCEPTABILITIES", "ACCEPTINGNESSES", "ACCESSARINESSES", "ACCESSIBILITIES", "ACCESSORINESSES", "ACCIDENTALITIES",
+		"ACCIDENTOLOGIES", "ACCLIMATISATION", "ACCLIMATIZATION", "ACCOMMODATINGLY", "ACCOMMODATIONAL", "ACCOMPLISHMENTS", "ACCOUNTABLENESS", "ACCOUNTANTSHIPS",
+		"ACCULTURATIONAL", "ACETOPHENETIDIN", "ACETYLSALICYLIC", "ACHONDROPLASIAS", "ACHONDROPLASTIC", "ACHROMATICITIES", "ACHROMATISATION", "ACHROMATIZATION",
+		"ACIDIMETRICALLY", "ACKNOWLEDGEABLE", "ACKNOWLEDGEABLY", "ACKNOWLEDGEMENT", "ACKNOWLEDGMENTS", "ACQUIRABILITIES", "ACQUISITIVENESS", "ACRIMONIOUSNESS",
+		"ACROPARESTHESIA", "ACTINOBIOLOGIES", "ACTINOCHEMISTRY", "ACTINOTHERAPIES", "ADAPTABLENESSES", "ADDITIONALITIES", "ADENOCARCINOMAS", "ADENOHYPOPHYSES",
+		"ADENOHYPOPHYSIS", "ADENOIDECTOMIES", "ADIATHERMANCIES", "ADJUSTABILITIES", "ADMINISTRATIONS", "ADMIRABLENESSES", "ADMISSIBILITIES", "ADRENALECTOMIES",
+		"ADSORBABILITIES", "ADVENTUROUSNESS", "ADVERSARINESSES", "ADVISABLENESSES", "AERODYNAMICALLY", "AERODYNAMICISTS", "AEROELASTICIANS", "AEROHYDROPLANES",
+		"AEROLITHOLOGIES", "AEROSOLISATIONS", "AEROSOLIZATIONS", "AFFECTABILITIES", "AFFECTIVENESSES", "AFFORDABILITIES", "AFFRANCHISEMENT", "AFTERSENSATIONS",
+		"AGGLUTINABILITY", "AGGRANDISEMENTS", "AGGRANDIZEMENTS", "AGGREGATENESSES", "AGRANULOCYTOSES", "AGRANULOCYTOSIS", "AGREEABLENESSES", "AGRIBUSINESSMAN",
+		"AGRIBUSINESSMEN", "AGRICULTURALIST", "AIRWORTHINESSES", "ALCOHOLISATIONS", "ALCOHOLIZATIONS", "ALCOHOLOMETRIES", "ALEXIPHARMAKONS", "ALGORITHMICALLY",
+		"ALKALINISATIONS", "ALKALINIZATIONS", "ALLEGORICALNESS", "ALLEGORISATIONS", "ALLEGORIZATIONS", "ALLELOMORPHISMS", "ALLERGENICITIES", "ALLOTETRAPLOIDS",
+		"ALLOTETRAPLOIDY", "ALLOTRIOMORPHIC", "ALLOWABLENESSES", "ALPHABETISATION", "ALPHABETIZATION", "ALTERNATIVENESS", "ALTITUDINARIANS", "ALUMINOSILICATE",
+		"ALUMINOTHERMIES", "AMARYLLIDACEOUS", "AMBASSADORSHIPS", "AMBIDEXTERITIES", "AMBIGUOUSNESSES", "AMBISEXUALITIES", "AMBITIOUSNESSES", "AMINOPEPTIDASES",
+		"AMINOPHENAZONES", "AMMONIFICATIONS", "AMORPHOUSNESSES", "AMPHIDIPLOIDIES", "AMPHITHEATRICAL", "ANACOLUTHICALLY", "ANACREONTICALLY", "ANAESTHESIOLOGY",
+		"ANAESTHETICALLY", "ANAGRAMMATISING", "ANAGRAMMATIZING", "ANALOGOUSNESSES", "ANALYZABILITIES", "ANAMORPHOSCOPES", "ANCYLOSTOMIASES", "ANCYLOSTOMIASIS",
+		"ANDROGYNOPHORES", "ANDROMEDOTOXINS", "ANDROMONOECIOUS", "ANDROMONOECISMS", "ANESTHETIZATION", "ANFRACTUOSITIES", "ANGUSTIROSTRATE", "ANIMATRONICALLY",
+		"ANISOTROPICALLY", "ANKYLOSTOMIASES", "ANKYLOSTOMIASIS", "ANNIHILATIONISM", "ANOMALISTICALLY", "ANOMALOUSNESSES", "ANONYMOUSNESSES", "ANSWERABILITIES",
+		"ANTAGONISATIONS", "ANTAGONIZATIONS", "ANTAPHRODISIACS", "ANTEPENULTIMATE", "ANTHROPOBIOLOGY", "ANTHROPOCENTRIC", "ANTHROPOGENESES", "ANTHROPOGENESIS",
+		"ANTHROPOGENETIC", "ANTHROPOLATRIES", "ANTHROPOLOGICAL", "ANTHROPOLOGISTS", "ANTHROPOMETRIES", "ANTHROPOMETRIST", "ANTHROPOMORPHIC", "ANTHROPOPATHIES",
+		"ANTHROPOPATHISM", "ANTHROPOPHAGIES", "ANTHROPOPHAGITE", "ANTHROPOPHAGOUS", "ANTHROPOPHOBIAS", "ANTHROPOPHOBICS", "ANTHROPOPHUISMS", "ANTHROPOPSYCHIC",
+		"ANTHROPOSOPHIES", "ANTHROPOSOPHIST", "ANTIABORTIONIST", "ANTIALCOHOLISMS", "ANTIAPHRODISIAC", "ANTIARRHYTHMICS", "ANTICAPITALISMS", "ANTICAPITALISTS",
+		"ANTICARCINOGENS", "ANTICHOLESTEROL", "ANTICHOLINERGIC", "ANTICHRISTIANLY", "ANTICLERICALISM", "ANTICLIMACTICAL", "ANTICOINCIDENCE", "ANTICOLONIALISM",
+		"ANTICOLONIALIST", "ANTICOMPETITIVE", "ANTICONVULSANTS", "ANTICONVULSIVES", "ANTIDEPRESSANTS", "ANTIDERIVATIVES", "ANTIDEVELOPMENT", "ANTIEDUCATIONAL",
+		"ANTIEGALITARIAN", "ANTIFASHIONABLE", "ANTIFEDERALISTS", "ANTIFERROMAGNET", "ANTIFORECLOSURE", "ANTIHELMINTHICS", "ANTIHISTAMINICS", "ANTILIBERALISMS",
+		"ANTILIBERTARIAN", "ANTILOGARITHMIC", "ANTIMATERIALISM", "ANTIMATERIALIST", "ANTIMETABOLITES", "ANTIMILITARISMS", "ANTIMILITARISTS", "ANTIMONARCHICAL",
+		"ANTIMONARCHISTS", "ANTIMONOPOLISTS", "ANTINATIONALIST", "ANTINUCLEARISTS", "ANTIODONTALGICS", "ANTIPERISTALSES", "ANTIPERISTALSIS", "ANTIPERISTALTIC",
+		"ANTIPERSPIRANTS", "ANTIPHLOGISTICS", "ANTIPORNOGRAPHY", "ANTIPROGRESSIVE", "ANTIQUARIANISMS", "ANTIRADICALISMS", "ANTIRATIONALISM", "ANTIRATIONALIST",
+		"ANTIRATIONALITY", "ANTIREPUBLICANS", "ANTIROMANTICISM", "ANTISEGREGATION", "ANTISENTIMENTAL", "ANTISEPARATISTS", "ANTISEPTICISING", "ANTISEPTICIZING",
+		"ANTISEXUALITIES", "ANTISHOPLIFTING", "ANTISOCIALITIES", "ANTISPECULATION", "ANTISPECULATIVE", "ANTISYPHILITICS", "ANTITHEORETICAL", "ANTITHROMBOTICS",
+		"ANTITRADITIONAL", "ANTITRANSPIRANT", "ANTITRINITARIAN", "ANTITUBERCULOUS", "ANTIVIVISECTION", "APHELIOTROPISMS", "APOCALYPTICALLY", "APOCALYPTICISMS",
+		"APOLIPOPROTEINS", "APOLITICALITIES", "APOPHTHEGMATISE", "APOPHTHEGMATIST", "APOPHTHEGMATIZE", "APOTHEGMATISING", "APOTHEGMATIZING", "APPEALABILITIES",
+		"APPEALINGNESSES", "APPENDICULARIAN", "APPLICABILITIES", "APPRENTICEHOODS", "APPRENTICEMENTS", "APPRENTICESHIPS", "APPROACHABILITY", "APPROPINQUATING",
+		"APPROPINQUATION", "APPROPINQUITIES", "APPROPRIATENESS", "ARACHNOIDITISES", "ARBITRARINESSES", "ARBORICULTURIST", "ARCHAEBACTERIUM", "ARCHAEOBOTANIES",
+		"ARCHAEOBOTANIST", "ARCHAEOMETRISTS", "ARCHAEOPTERYXES", "ARCHAEZOOLOGIES", "ARCHEOASTRONOMY", "ARCHEOBOTANISTS", "ARCHEOLOGICALLY", "ARCHEOMAGNETISM",
+		"ARCHEOZOOLOGIES", "ARCHEOZOOLOGIST", "ARCHGENETHLIACS", "ARCHIDIACONATES", "ARCHIEPISCOPACY", "ARCHIEPISCOPATE", "ARCHITECTURALLY", "ARCHPRIESTHOODS",
+		"ARCHPRIESTSHIPS", "ARGUMENTATIVELY", "ARIBOFLAVINOSES", "ARIBOFLAVINOSIS", "AROMATHERAPISTS", "ARRONDISSEMENTS", "ARTERIALISATION", "ARTERIALIZATION",
+		"ARTERIOGRAPHIES", "ARTIFICIALISING", "ARTIFICIALITIES", "ARTIFICIALIZING", "ASCLEPIADACEOUS", "ASSENTIVENESSES"}
+
 	for i := 0; i < b.N; i++ {
-		CopyIn("temp", bigTableColumns...)
+		_ = CopyIn("temp", bigTableColumns...)
 	}
 }

internal/pqsql/copy.go

@@ -0,0 +1,37 @@
+package pqsql
+
+// StartsWithCopy reports if the SQL strings start with "copy", ignoring
+// whitespace, comments, and casing.
+func StartsWithCopy(query string) bool {
+	if len(query) < 4 {
+		return false
+	}
+	var linecmt, blockcmt bool
+	for i := 0; i < len(query); i++ {
+		c := query[i]
+		if linecmt {
+			linecmt = c != '\n'
+			continue
+		}
+		if blockcmt {
+			blockcmt = !(c == '/' && query[i-1] == '*')
+			continue
+		}
+		if c == '-' && len(query) > i+1 && query[i+1] == '-' {
+			linecmt = true
+			continue
+		}
+		if c == '/' && len(query) > i+1 && query[i+1] == '*' {
+			blockcmt = true
+			continue
+		}
+		if c == ' ' || c == '\t' || c == '\r' || c == '\n' {
+			continue
+		}
+
+		// First non-comment and non-whitespace.
+		return len(query) > i+3 && c|0x20 == 'c' && query[i+1]|0x20 == 'o' &&
+			query[i+2]|0x20 == 'p' && query[i+3]|0x20 == 'y'
+	}
+	return false
+}

internal/pqsql/copy_test.go

@@ -0,0 +1,53 @@
+package pqsql
+
+import (
+	"testing"
+)
+
+func TestStartsWithCopy(t *testing.T) {
+	tests := []struct {
+		input string
+		want  bool
+	}{
+		{"COPY data;", true},
+		{"copy data;", true},
+		{"   COPY", true},
+		{"-- comment only\nCOPY table", true},
+		{"/* comment */COPY table", true},
+		{"/* comment */  COPY table", true},
+		{"-- comment only\n/* and another */COPY table", true},
+		{"\n\n/* header */  COPY my_table FROM stdin;", true},
+		{"  -- some comment\n /* block */  COPY table FROM stdin;", true},
+		{"SELECT * FROM users;", false},
+		{"-- some comment not terminated on purpose (or not) COPY table FROM stdin;", false},
+		{"-- COPY table FROM stdin;\nSELECT * FROM users;", false},
+
+		{"", false},
+		{"c", false},
+		{"co", false},
+		{"cop", false},
+		{"copy", true},
+		{"/", false},
+		{"/*", false},
+		{"/* *", false},
+		{"/* */", false},
+		{"-", false},
+		{"--", false},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.input, func(t *testing.T) {
+			have := StartsWithCopy(tt.input)
+			if have != tt.want {
+				t.Errorf("want %v; have %v", tt.want, have)
+			}
+		})
+	}
+}
+
+func BenchmarkStartsWithCopy(b *testing.B) {
+	sql := "  -- comment\n /* block */ \n COPY table FROM stdin;"
+	for i := 0; i < b.N; i++ {
+		_ = StartsWithCopy(sql)
+	}
+}